Detecting activations in PET and fMRI: levels of inference and power

Structural neural networks subserving oculomotor function in first-episode schizophrenia

BACKGROUND

Smooth pursuit and antisaccade abnormalities are well documented in schizophrenia, but their neuropathological correlates remain unclear.

METHODS

In this study, we used statistical parametric mapping to investigate the relationship between oculomotor abnormalities and brain structure in a sample of first-episode schizophrenia patients (n = 27). In addition to conventional volumetric magnetic resonance imaging, we also used magnetization transfer ratio, a technique that allows more precise tissue characterization.

RESULTS

We found that smooth pursuit abnormalities were associated with reduced magnetization transfer ratio in several regions, predominantly in the right prefrontal cortex. Antisaccade errors correlated with gray matter volume in the right medial superior frontal cortex as measured by conventional magnetic resonance imaging but not with magnetization transfer ratio.

CONCLUSIONS

These preliminary results demonstrate that specific structural abnormalities are associated with abnormal eye movements in schizophrenia.

Reference Frames for Spatial Cognition: Different Brain Areas are Involved in Viewer-, Object-, and Landmark-Centered Judgments About Object Location

Functional magnetic resonance imaging was used to compare the neural correlates of three different types of spatial coding, which are implicated in crucial cognitive functions of our everyday life, such as visuomotor coordination and orientation in topographical space. By manipulating the requested spatial reference during a task of relative distance estimation, we directly compared viewer-centered, object-centered, and landmark-centered spatial coding of the same realistic 3-D information. Common activation was found in bilateral parietal, occipital, and right frontal premotor regions.

The retrosplenial and ventromedial occipital–temporal cortex (and parts of the parietal and occipital cortex) were significantly more activated during the landmark-centered condition. The ventrolateral occipital–temporal cortex was particularly involved in object-centered coding. Results strongly demonstrate that viewer-centered (egocentric) coding is restricted to the dorsal stream and connected frontal regions, whereas a coding centered on external references requires both dorsal and ventral regions, depending on the reference being a movable object or a landmark.

Comparing methods of analyzing fMRI statistical parametric maps

Approaches for the analysis of statistical parametric maps (SPMs) can be crudely grouped into three main categories in which different philosophies are applied to delineate activated regions. These being type I error control thresholding, false discovery rate (FDR) control thresholding and posterior probability thresholding. To better understand the properties of these main approaches, we carried out a simulation study to compare the approaches as they would be used on real data sets. Using default settings, we find that posterior probability thresholding is the most powerful approach, and type I error control thresholding provides the lowest levels of type I error. False discovery rate control thresholding performs in between the other approaches for both these criteria, although for some parameter settings this approach can approximate the performance of posterior probability thresholding. Based on these results, we discuss the relative merits of the three approaches in an attempt to decide upon an optimal approach. We conclude that viewing the problem of delineating areas of activation as a classification problem provides a highly interpretable framework for comparing the methods. Within this framework, we highlight the role of the loss function, which explicitly penalizes the types of errors that may occur in a given analysis.

Neural Basis of Genetically Determined Visuospatial Construction Deficit in Williams Syndrome

A unique opportunity to understand genetic determinants of cognition is offered by Williams syndrome (WS), a well-characterized hemideletion on chromosome 7q11.23 that causes extreme, specific weakness in visuospatial construction (the ability to visualize an object as a set of parts or construct a replica). Using multimodal neuroimaging, we identified a neural mechanism underlying the WS visuoconstructive deficit. Hierarchical assessment of visual processing with fMRI showed isolated hypoactivation in WS in the parietal portion of the dorsal stream. In the immediately adjacent parietooccipital/intraparietal sulcus, structural neuroimaging showed a gray matter volume reduction in participants with WS. Path analysis demonstrated that the functional abnormalities could be attributed to impaired input from this structurally altered region. Our observations confirm a longstanding hypothesis about dorsal stream dysfunction in WS, demonstrate effects of a localized abnormality on visual information processing in humans, and define a systems-level phenotype for mapping genetic determinants of visuoconstructive function.

Combining voxel intensity and cluster extent with permutation test framework

In a massively univariate analysis of brain image data, statistical inference is typically based on intensity or spatial extent of signals. Voxel intensity-based tests provide great sensitivity for high intensity signals, whereas cluster extent-based tests are sensitive to spatially extended signals. To benefit from the strength of both, the intensity and extent information needs to be combined. Various ways of combining voxel intensity and cluster extent are possible, and a few such combining methods have been proposed. Poline et al.'s [NeuroImage 16 (1997) 83] minimum P value approach is sensitive to signals whose either intensity or extent is significant. Bullmore et al.'s [IEEE Trans. Med. Imag. 18 (1999) 32] cluster mass method can detect signals whose intensity and extent are sufficiently large, even when they are not significant by intensity or extent alone. In this work, we study such combined inference methods using combining functions (Pesarin, F., 2001. Multivariate Permutation Tests. Wiley, New York) and permutation framework [Holmes et al., J. Cereb. Blood Flow Metab. 16 (1996) 7], which allow us to examine different ways of combining voxel intensity and cluster extent information without knowing their distribution. We also attempt to calibrate combined inference by using weighted combining functions, which adjust the test according to signals of interest. Furthermore, we propose meta-combining, a combining function of combining functions, which integrates strengths of multiple combining functions into a single statistic. We found that combined tests are able to detect signals that are not detected by voxel or cluster size test alone. We also found that the weighted combining functions can calibrate the combined test according to the signals of interest, emphasizing either intensity or extent as appropriate. Though not necessarily more sensitive than individual combining functions, the meta-combining function is sensitive to all types of signals and thus can be used as a single test summarizing all the combining functions.

Modulation of cerebellar activities by acupuncture stimulation: evidence from fMRI study

Recent neuroimaging studies have revealed that acupuncture stimulation modulates human central nervous system including cerebral limbic/paralimbic and subcortical structures. Due to the wide and intricate connections with cerebrum, we hypothesized that anatomically specific areas in human cerebellum are also modulated by acupuncture stimulation beyond classical involvement of cerebellum in motor coordination. Functional MRI (fMRI) was used to investigate neural substrates responding to the acupuncture stimulation of Pericardium 6 (PC6, Neiguan), an acupoint relevant for the management of nausea including vestibular-related motion sickness. Sham stimulation near the acupoint and tactile stimulation on the skin of the acupoint were given as separate conditions. Psychophysical scores as well as the heart and respiratory rates were measured during each condition. Acupuncture manipulation on PC6, in comparison to the sham acupuncture and tactile stimulation conditions, selectively activated left superior frontal gyrus, anterior cingulate gyrus, and dorsomedial nucleus of thalamus. Acupuncture-specific neural substrates in cerebellum were also evident in declive, nodulus, and uvula of vermis, quadrangular lobule, cerebellar tonsil, and superior semilunar lobule. Negative MR signal changes, often seen during the acupuncture of analgesic points, were not observed in the present study. Our data suggest that cerebellum serves as important activation loci during the acupuncture stimulation of PC6, and clinical efficacy of PC6 may be mediated by the cerebellar vestibular neuromatrix.

Phonemic manipulation in Japanese: an fMRI study

Phonological awareness is the ability to manipulate abstract phonological representations of language and is crucial to the process of learning to read. The neural substrates underlying this appear to be modality-independent at least in alphabetic languages. Japanese language has different orthographic "kana" system, in which each "kana" character strictly corresponds to a syllable. To investigate the neural substrates underlying phonological manipulation of the Japanese language, functional magnetic resonance imaging (fMRI) was used. Neuroimaging data were obtained from adult healthy volunteers during auditory and visual vowel exchange tasks, identical except for the modality of stimuli presentation: a voice and Japanese "kana" characters. Cerebellar vermis was activated by vowel exchange tasks of both modalities. The posterior parts of the superior temporal sulcus (STS) were active during the auditory tasks, suggesting that phonological representations of auditory stimuli are manipulated in this area. These findings are consistent with the previous studies with alphabetic languages. In contrast, the intraparietal sulci, which has been implicated for visuospatial tasks, was active during the visual tasks. This modality-dependent activation may indicate that the simple orthographic rule of the Japanese allows an alternate visual strategy to conduct the phonological awareness task, bypassing manipulation of phonological representation.

A [17F]-fluoromethane PET/TMS study of effective connectivity

We used transcranial magnetic stimulation (TMS) in combination with positron emission tomography (PET) to investigate the effective connectivity of four cortical regions within the same study. By employing [17F]-[CH3F] ([17F]-fluoromethane) as a radiotracer of blood-flow, we were able to obtain increased sensitivity compared to [15O]-H2O for both cortical and subcortical structures. The brain areas investigated were left primary motor cortex, right primary visual cortex, and left and right prefrontal areas. We found that each site of stimulation yielded a different pattern of activation/deactivation consistent with its anatomical connectivity. Moreover, we found that TMS of prefrontal and motor cortical areas gave rise to trans-synaptic activation of subcortical circuits.

Acute Bilateral Basal Ganglia Lesions in Patients With Diabetic Uremia: An FDG-PET Study

PURPOSE

Head CT and MRI show characteristic changes in the syndrome of acute bilateral basal ganglia lesions in patients with diabetic uremia. However, they do not provide further insight into the underlying pathophysiology. To further clarify the biologic mechanism of the syndrome, F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) was used in 2 patients.

METHODS

PET studies were performed in 2 diabetic uremic patients with acute movement disorders. The cerebral glucose metabolic rates in these 2 patients were compared with 11 normal age-matched controls. The images were further analyzed with statistical parametric mapping to identify regions of significant metabolic abnormality.

RESULTS

The cases showed markedly reduced glucose metabolism in the bilateral basal ganglia, especially in the bilateral putamens, where the glucose uptake was nearly absent.

CONCLUSIONS

FDG-PET correlates better with the clinical conditions and provides more pathophysiological information than head CT or MRI scans in bilateral basal ganglia lesions in patients with diabetic uremia. We propose that acute exacerbation of a long-term glucose utilization failure in the basal ganglia cells produced these lesions.

Learned audio-visual cross-modal associations in observed piano playing activate the left planum temporale. An fMRI study

Lip reading is known to activate the planum temporale (PT), a brain region which may integrate visual and auditory information. To find out whether other types of learned audio-visual integration occur in the PT, we investigated "key-touch reading" using functional magnetic resonance imaging (fMRI). As well-trained pianists are able to identify pieces of music by watching the key-touching movements of the hands, we hypothesised that the visual information of observed sequential finger movements is transformed into the auditory modality during "key-touch reading" as is the case during lip reading. We therefore predicted activation of the PT during key-touch reading. Twenty-six healthy right-handed volunteers were recruited for fMRI. Of these, 7 subjects had never experienced piano training (naïve group), 10 had a little experience of piano playing (less trained group), and the remaining 9 had been trained for more than 8 years (well trained group). During task periods, subjects were required to view the bimanual hand movements of a piano player making key presses. During control periods, subjects viewed the same hands sliding from side to side without tapping movements of the fingers. No sound was provided. Sequences of key presses during task periods consisted of pieces of familiar music, unfamiliar music, or random sequences. Well-trained subjects were able to identify the familiar music, whereas less-trained subjects were not. The left PT of the well-trained subjects was equally activated by observation of familiar music, unfamiliar music, and random sequences. The naïve and less trained groups did not show activation of the left PT during any of the tasks. These results suggest that PT activation reflects a learned process. As the activation was elicited by viewing key pressing actions regardless of whether they constituted a piece of music, the PT may be involved in processes that occur prior to the identification of a piece of music, that is, mapping the complex sequence structure of hand movements onto the sequence of sounds.

Simplification of analysis procedures in inter-subject studies with cardiac PET imaging

Quantitative analysis in positron emission tomography imaging usually necessitates several studies carried out under the same protocol in order to get functional or metabolic parameter values with low variations. Apart from subject preparation and measurements in similar conditions, the data analysis should be done as uniformly as possible. In this work we report PET data obtained in normal and ischemic rats, measured with (13)N-ammonia and (11)C-acetate to extract myocardial blood flow and oxygen consumption, and analysed with the usual region of interest (ROI) drawing method in each rat individually, in comparison to a new method based on resampling all the rat heart images to a common model, then the ROIs are drawn once and copied onto each rat image sequence.

Nonstationary cluster-size inference with random field and permutation methods

Because of their increased sensitivity to spatially extended signals, cluster-size tests are widely used to detect changes and activations in brain images. However, when images are nonstationary, the cluster-size distribution varies depending on local smoothness. Clusters tend to be large in smooth regions, resulting in increased false positives, while in rough regions, clusters tend to be small, resulting in decreased sensitivity. Worsley et al. proposed a random field theory (RFT) method that adjusts cluster sizes according to local roughness of images [Worsley, K.J., 2002. Nonstationary FWHM and its effect on statistical inference of fMRI data. Presented at the 8th International Conference on Functional Mapping of the Human Brain, June 2-6, 2002, Sendai, Japan. Available on CD-ROM in NeuroImage 16 (2) 779-780; Hum. Brain Mapp. 8 (1999) 98]. In this paper, we implement this method in a permutation test framework, which requires very few assumptions, is known to be exact [J. Cereb. Blood Flow Metab. 16 (1996) 7] and is robust [NeuroImage 20 (2003) 2343]. We compared our method to stationary permutation, stationary RFT, and nonstationary RFT methods. Using simulated data, we found that our permutation test performs well under any setting examined, whereas the nonstationary RFT test performs well only for smooth images under high df. We also found that the stationary RFT test becomes anticonservative under nonstationarity, while both nonstationary RFT and permutation tests remain valid under nonstationarity. On a real PET data set we found that, though the nonstationary tests have reduced sensitivity due to smoothness estimation variability, these tests have better sensitivity for clusters in rough regions compared to stationary cluster-size tests. We include a detailed and consolidated description of Worsley nonstationary RFT cluster-size test.

fMRI evidence of brain reorganization during attention and memory tasks in multiple sclerosis

Functional magnetic resonance imaging (fMRI) data on motor function have shown adaptive functional changes related to brain injury in multiple sclerosis (MS). We investigated whether patients with MS have altered fMRI activation patterns during attention and memory tasks, and whether functional changes in the brain correlate with the extent of overall tissue damage on conventional MRI. Twenty-two right-handed patients with relapsing-remitting MS (RRMS) and no or only mild deficits at neuropsychological testing and 22 matched healthy subjects were scanned during the Paced Auditory Serial Addition Test (PASAT) and a recall task. fMRI data were analyzed using Statistical Parametric Mapping (SPM99). The relation between fMRI changes during both tasks and T2 lesion load was investigated. During both tasks, patients exhibited significantly greater brain activation than controls and recruited additional brain areas. Task-related functional changes were more significant in patients whose performance matched that of controls than in patients with a lower performance. During the PASAT, brain functional changes involved the right supplementary motor area and cingulate, the bilateral prefrontal, temporal and parietal areas, whereas during the recall task they involved the prefrontal and temporal cortex and basal ganglia bilaterally, and the left thalamus. In patients, activation in specific brain areas during performance of both tasks positively correlated with T2 brain lesions. Patients with RRMS exhibit altered patterns of activation during tasks exploring sustained attention, information processing and memory. During these tasks, fMRI activity is greater in patients with better cognitive function than in those with lower cognitive function. Functional changes in specific brain areas increase with increasing tissue damage suggesting that they may also represent adaptive mechanisms that reflect underlying neural disorganization or disinhibition, possibly associated with MS.

Different areas of human non-primary auditory cortex are activated by sounds with spatial and nonspatial properties

In humans, neuroimaging studies have identified the planum temporale to be particularly responsive to both spatial and nonspatial attributes of sound. However, a functional segregation of the planum temporale along these acoustic dimensions has not been firmly established. We evaluated this scheme in a factorial design using modulated sounds that generated a percept of motion (spatial) or frequency modulation (nonspatial). In addition, these sounds were presented in the context of a motion detection and a frequency-modulation detection task to investigate the cortical effects of directing attention to different perceptual attributes of the sound. Motion produced stronger activation in the medial part of the planum temporale and frequency-modulation produced stronger activation in the lateral part of the planum temporale, as well as an additional non-primary area lateral to Heschl's gyrus. These separate subregions are consistent with the notion of divergent processing streams for spatial and nonspatial auditory information. Activation in the superior parietal cortex, putatively involved in the spatial pathway, was dependent on the task of motion detection and not simply on the presence of acoustic cues for motion. This finding suggests that the listening task is an important determinant of how the processing stream is engaged.

Acute vagus nerve stimulation using different pulse widths produces varying brain effects

BACKGROUND

Vagus nerve stimulation (VNS) is an approved treatment for epilepsy and has been investigated in clinical trials of depression. Little is known about the relationship of VNS parameters to brain function. Using the interleaved VNS /functional magnetic resonance imaging (fMRI) technique, we tested whether variations of VNS pulse width (PW) would produce different immediate brain activation in a manner consistent with single neuron PW studies.

METHODS

Twelve adult patients with major depression, treated with VNS, underwent three consecutive VNS/fMRI scans, each randomly using one of three PWs (130 micros, 250 micros, or 500 micros). The data were analyzed with SPM2.

RESULTS

Global activations induced by PWs 250 and 500 were both significantly greater than that induced by PW 130 but not significantly different from each other. For global deactivation, PWs 130 and 250 were both significantly greater than PW 500 but not significantly different from each other. Regional similarities and differences were also seen with the various PWs.

CONCLUSIONS

The data confirm our hypothesis that VNS at PW 500 globally produces no more activation than does PW 250, and PW 130 is insufficient for activation of some regions. These data suggest that PW is an important variable in producing VNS brain effects.

Positive and negative network correlations in temporal lobe epilepsy

Temporal lobe seizures are accompanied by complex behavioral phenomena including loss of consciousness, dystonic movements and neuroendocrine changes. These phenomena may arise from extended neural networks beyond the temporal lobe. To investigate this, we imaged cerebral blood flow (CBF) changes during human temporal lobe seizures with single photon emission computed tomography (SPECT) while performing continuous video/EEG monitoring. We found that temporal lobe seizures associated with loss of consciousness produced CBF increases in the temporal lobe, followed by increases in bilateral midline subcortical structures. These changes were accompanied by marked bilateral CBF decreases in the frontal and parietal association cortex. In contrast, temporal lobe seizures in which consciousness was spared were not accompanied by these widespread CBF changes. The CBF decreases in frontal and parietal association cortex were strongly correlated with increases in midline structures such as the mediodorsal thalamus. These results suggest that impaired consciousness in temporal lobe seizures may result from focal abnormal activity in temporal and subcortical networks linked to widespread impaired function of the association cortex.

Frontal lobe gray matter density decreases in bipolar I disorder

BACKGROUND

This study was conducted to explore differences in gray and white matter density between bipolar and healthy comparison groups using voxel-based morphometry (VBM).

METHODS

Brain magnetic resonance imaging was performed for 39 subjects with bipolar I disorder and 43 comparison subjects. Images were registered into a proportional stereotaxic space and segmented into gray matter, white mater, and cerebrospinal fluid. Statistical parametric mapping was used to calculate differences in gray and white matter density between groups.

RESULTS

Bipolar subjects had decreased gray matter density in left anterior cingulate gyrus (Brodmann's area [BA] 32, 7.3% decrease), an adjacent left medial frontal gyrus (BA 10, 6.9% decrease), right inferior frontal gyrus (BA 47, 9.2% decrease), and right precentral gyrus (BA 44, 6.2% decrease), relative to comparison subjects.

CONCLUSIONS

The observation of a gray matter density decrease in the left anterior cingulate, which processes emotions, in bipolar subjects is consistent with prior reports that used region-of-interest analytic methods. Decreased gray matter density in the right inferior frontal gyrus, which processes nonverbal and intrinsic functions, supports nondominant hemisphere dysfunction as a component of bipolar disorder.

Alcohol intoxication effects on visual perception: an fMRI study

We examined the effects of two doses of alcohol (EtOH) on functional magnetic resonance imaging (fMRI) activation during a visual perception task. The Motor-Free Visual Perception Test-Revised (MVPT-R) provides measures of overall visual perceptual processing ability. It incorporates different cognitive elements including visual discrimination, spatial relationships, and mental rotation. We used the MVPT-R to study brain activation patterns in healthy controls (1) sober, and (2) at two doses of alcohol intoxication with event-related fMRI. The fMRI data were analyzed using a general linear model approach based upon a model of the time course and a hemodynamic response estimate. Additionally, a correlation analysis was performed to examine dose-dependent amplitude changes. With regard to alcohol-free task-related brain activation, we replicate our previous finding in which SPM group analysis revealed robust activation in visual and visual association areas, frontal eye field (FEF)/dorsolateral prefrontal cortex (DLPFC), and the supplemental motor area (SMA). Consistent with a previous study of EtOH and visual stimulation, EtOH resulted in a dose-dependent decrease in activation amplitude over much of the visual perception network and in a decrease in the maximum contrast-to-noise ratio (in the lingual gyrus). Despite only modest behavior changes (in the expected direction), significant dose-dependent activation increases were observed in insula, DLPFC, and precentral regions, whereas dose-dependent activation decreases were observed in anterior and posterior cingulate, precuneus, and middle frontal areas. Some areas (FEF/DLPFC/SMA) became more diffusely activated (i.e., increased in spatial extent) at the higher dose. Alcohol, thus, appears to have both global and local effects upon the neural correlates of the MVPT-R task, some of which are dose dependent.

Focal network involvement in generalized seizures: new insights from electroconvulsive therapy

Generalized seizures are commonly thought to involve the entire brain homogeneously. However, recent evidence suggests that selective cortical-subcortical networks may be crucial for the initiation, propagation, and behavioral manifestations of generalized seizures, while other brain regions are relatively spared. Here we review previous studies, and describe a new human model system for the investigation of generalized seizures: single-photon emission computed tomography, ictal-interictal difference imaging of generalized tonic-clonic seizures induced by electroconvulsive therapy (ECT). Bitemporal ECT activates focal bilateral frontotemporal and parietal association cortex, sparing other regions; bifrontal ECT activates mainly prefrontal cortex; while in right unilateral ECT the left frontotemporal region is relatively spared. Associated midline subcortical networks are also involved. Focal verbal memory deficits parallel the focal regions involved in these neuroimaging studies. Further studies of this kind may elucidate specific networks in generalized tonic-clonic seizures, providing targets for new therapeutic interventions in epilepsy.

Differential Cortical and Subcortical Activations in Learning Rotations and Gains for Reaching: A PET Study

Previous studies suggest that horizontal reaching movements are planned vectorially with independent specification of direction and extent. The transformation from visual to hand-centered coordinates requires the learning of a task-specific reference frame and scaling factor. We studied learning of a novel reference frame by imposing a screen-cursor rotation and learning of a scaling factor by imposing a novel gain. Previous work demonstrates that rotation and gain learning have different time courses and patterns of generalization. Here we used PET to identify and compare brain areas activated during rotation and gain learning, with a baseline motor-execution task as the subtracted control. Previous work has shown that the time courses of rotation and gain adaptation have a short rapid phase followed by a longer slow phase. We therefore also sought to compare activations associated with the rapid and slower phases of adaptation. We isolated the rapid phase by alternating opposite values of the rotation or gain every 16 movements. The rapid phase of rotation adaptation activated the preSMA. More complete adaptation to the rotation activated right ventral premotor cortex, right posterior parietal cortex, and the left lateral cerebellum. The rapid phase of gain learning only activated subcortical structures: bilateral putamen and left cerebellum. More complete gain learning failed to show any significant activation. We conclude that the time course of rotation adaptation is paralleled by a frontoparietal shift in activated cortical regions. In contrast, early gain adaptation involves only subcortical structures, which we suggest reflects a more automatic process of contextual recalibration of a scaling factor.

Human cerebral activation during steady-state visual-evoked responses

Flicker stimuli of variable frequency (2-90 Hz) elicit a steady-state visual-evoked response (SSVER) in the electroencephalogram (EEG) with the same frequency as the stimulus. In humans, the amplitude of this response peaks at approximately 15 Hz, decreasing at higher stimulation frequencies. It was not known whether this peak response corresponds to increased synaptic activity in the visual cortex or to other mechanisms [for instance, the temporal coherence (phase summation) of evoked responses]. We studied the SSVER in 16 normal volunteers by means of visual stimulation at 14 different frequencies (from 5 to 60 Hz) while recording the EEG. In nine subjects of the group, we measured regional cerebral blood flow (rCBF) with positron emission tomography (PET)-H2(15)O at rest and during visual stimulation at five different frequencies: 5, 10, 15, 25, and 40 Hz. We confirmed that the amplitude of the SSVER in occipital regions peaks at 15 Hz stimulation. Applying to the PET rCBF data a contrast weighted by the amplitude of the SSVER, we determined that the primary visual cortex rCBF follows an activation pattern similar to the SSVER. This finding suggests that the amplitude of the SSVER corresponds to increased synaptic activity, specifically in Brodmann's area 17. Additionally, this study showed that visual stimulation at 40 Hz causes selective activation of the macular region of the visual cortex, and that a region in the dorsal aspect of the Crus I lobule of the left cerebellar hemisphere is activated during repetitive visual stimulation.

Clozapine but not haloperidol Re-establishes normal task-activated rCBF patterns in schizophrenia within the anterior cingulate cortex

Our previous work has identified that unmedicated volunteers with schizophrenia have regional cerebral blood flow (rCBF) activation patterns inappropriately related to the cognitive demand of a task in anterior cingulate cortex (ACC). Using positron emission tomography (PET) with (15)O water, we compared task-induced rCBF patterns induced by haloperidol or clozapine in individuals with schizophrenia. We hypothesized that clozapine, given its superior clinical action, would tend to normalize the abnormal task-activated response in ACC more than haloperidol. Schizophrenia volunteers (SVs) (n=6) and normal volunteers (NVs) (n=12) were trained to perform a tone discrimination task with 70-80% accuracy. They were then scanned during three task conditions: (1). Rest, (2). sensory motor control (SMC) task, and (3). decision task (DEC). SVs were initially scanned after withdrawal of all psychotropic medication and again after treatment with therapeutic doses of haloperidol (n=5) and/or clozapine (n=5). rCBF values, sampled in the grown maxima of the task-activated ACC cluster, were analyzed between groups and task conditions. Task performance was similar across the unmedicated, haloperidol- and clozapine-medicated SV groups. There was a reduction in accuracy in the haloperidol SV group compared to the NVs. Group and task conditions affected rCBF in the ACC. Clozapine, but not haloperidol, reversed the abnormal ACC rCBF pattern in unmedicated SV to normal. The clozapine-treated SV group showed a rCBF pattern similar to the NV group in that ACC activation was not observed during the control task but occurred during the decision condition. The pattern seen in the haloperidol-treated SV group was similar to the unmedicated SV group in that ACC activation was seen during the control task and no further activation was seen during the DEC. We report that clozapine, but not haloperidol, normalizes anterior cingulate rCBF patterns in schizophrenia during a cognitive task. Based on these preliminary data, we propose that this pattern may account for the superior therapeutic effect of clozapine and represents a surrogate marker of this action.

Electrophysiological evidence of corollary discharge dysfunction in schizophrenia during talking and thinking

Failure of corollary discharge, a mechanism for distinguishing self-generated from externally-generated percepts, has been posited to underlie certain positive symptoms of schizophrenia, including auditory hallucinations. Although originally described in the visual system, corollary discharge may exist in the auditory system, whereby signals from motor speech commands prepare auditory cortex for self-generated speech. While associated with sensorimotor systems, it might also apply to inner speech or thought, regarded as our most complex motor act. We had four aims in the studies summarized in this paper: (1) to demonstrate the corollary discharge phenomenon during talking and inner speech in human volunteers using event-related brain potentials (ERPs), (2) to demonstrate that the corollary discharge is abnormal in patients with schizophrenia, (3) to demonstrate the role of frontal speech areas in the corollary discharge during talking, and (4) to relate the dysfunction of the corollary discharge in schizophrenia to auditory hallucinations. Using EEG and ERP measures, we addressed each aim in patients with schizophrenia (DSM IV) and healthy control subjects. The N1 component of the ERP reflected dampening of auditory cortex responsivity during talking and inner speech in control subjects but not in patients. EEG measures of coherence indicated inter-dependence of activity in the frontal speech production and temporal speech reception areas during talking in control subjects, but not in patients, especially those who hallucinated. These data suggest that a corollary discharge from frontal areas where thoughts are generated fails to alert auditory cortex that they are self-generated, leading to the misattribution of inner speech to external sources and producing the experience of auditory hallucinations.

Effects of 1-Hz repetitive transcranial magnetic stimulation on acute pain induced by capsaicin

The aim of this study is to investigate the efficacy of 1-Hz repetitive transcranial magnetic stimulation (rTMS) over the primary motor cortex (M1) on acute pain induced by intradermal capsaicin injection and to elucidate its mechanisms by single-photon emission computed tomography (SPECT). We compared time courses of a subjective scale of pain induced by intradermal capsaicin injection in seven normal subjects under three different conditions: rTMS over M1, sham stimulation, and control condition (natural course of acute pain without any stimulation). In ten normal subjects, using SPECT, we also studied differences in regional cerebral blood flow (rCBF) after capsaicin injection between two conditions: rTMS over M1 and the control condition. rTMS over M1 induced earlier recovery from acute pain compared with the sham or control conditions. Under rTMS over the right M1 condition compared with the control condition, the SPECT study demonstrated a significant relative rCBF decrease in the right medial prefrontal cortex (MPFC) corresponding to Brodmann area (BA) 9, and a significant increase in the caudal part of the right anterior cingulate cortex (ACC) corresponding to BA24 and the left premotor area (BA6). A region-of-interest analysis showed significant correlation between pain reduction and rCBF changes in both BA9 and BA24. We conclude that rTMS over M1 should have beneficial effects on acute pain, and its effects must be caused by functional changes of MPFC and caudal ACC.

Evidence of enhancement of spatial attention during inhibition of a visuo-motor response

A visuo-motor task was used as the setting for a study into inhibition in six healthy volunteers using fMRI. The task involved responding to colored stimuli, which appeared at random positions in the left and right visual field, with the corresponding hand. The volunteers were asked to respond to green colored stimuli ("go" response) and to inhibit responses to red stimuli ("no-go" response). The task was presented in a block design with blocks of three types; only "go" trials, a pseudo-random mixture of "go" and "no-go" tasks ("go/no-go" block), and "visual control." ANCOVA analysis of the fMRI data was performed within the framework of SPM99. Increased activation in the go vs visual control comparison was found in the bilateral motor and medial premotor cortices associated with the action of the button press response, as well as parietal regions attending to the task of identifying the visual field. The go/no-go vs visual control comparison showed a similar pattern, plus additional prefrontal areas that have previously been shown to be associated with inhibition. The direct comparison of the go and go/no-go blocks highlighted large differences not only in the prefrontal cortices, associated with inhibition, but also particularly in the right parietal cortex. We interpret the increased parietal activation, during inhibition, as representing a heightened spatial attention required for the correct execution of the inhibition task.

Gender differences in patterns of cerebral activation during equal experience of painful laser stimulation

A previous functional imaging study demonstrated greater female response in the anterior insula and thalamus and left prefrontal activation in men and right prefrontal activation in women during equal heat intensity but unequal pain experience. For the current study, subjective intensities of noxious heat delivered to the back of the right hand were equalized across subjects, and regional cerebral blood flow was recorded by using positron emission tomography. The female subjects required less laser energy before reporting pain, but the difference was not significant. Correlation of regional cerebral blood flow with subjective pain experience in the whole group showed significant bilateral responses in the parietal, lateral premotor, prefrontal, secondary somatosensory, anterior cingulate and insula cortices, as well as the thalamus. There was significantly greater activation in the left, contralateral, prefrontal, primary and secondary somatosensory, parietal, and insula cortices in the male subjects compared with the female subjects and greater response in the perigenual cingulate cortex in the female subjects. Our study is the first to associate consistent pain experience with gender differences in central response. These differences may relate to differential processing of acute pain with implications for clinical disorders that show a female dominance. The subtle behavioral differences and inconsistent findings across studies, however, suggest the need for caution and further experimentation before speculating further.

Reduced cortical gray matter density in human MDMA (Ecstasy) users: a voxel-based morphometry study

The popular recreational drug, 3,4-methylenedioxymethamphetamine (MDMA) exerts its actions in part via blockade of serotonin and dopamine reuptake. Many animal and human studies have demonstrated long-lasting reductions in measures of central nervous system (CNS) serotonin function following MDMA administration. One emerging role of serotonin function in the CNS is a positive trophic effect via stimulation of intracellular signaling pathways and trophic factors. We hypothesized that human MDMA users might display neocortical gray matter reductions due to loss of serotonergically mediated trophic effects on cortical cells. However, unlike animal models, most human MDMA users worldwide are polydrug users, thereby complicating the assessment of MDMA toxicity in this group. Structural magnetic resonance imaging (MRI) scans of 31 MDMA polydrug users versus 29 non-MDMA users were compared using voxel-based morphometry (VBM) to assess regional brain gray and white matter concentration. VBM employs gray/white matter segmentation and statistical parametric mapping (SPM) analysis to calculate a voxel-wise comparison of regional gray or white matter concentration. Using this method, we consistently found several brain regions having decreased gray matter concentration in MDMA polydrug users. These regions were localized to neocortex in bilateral Brodmann area (BA) 18, left BA 21, and left BA 45, as well as bilateral cerebellum, and midline brainstem. Overall, these preliminary findings suggest that MDMA polydrug users have multiple regions of gray matter reduction, potentially accounting for previously reported neuropsychiatric impairments in MDMA users. Additional animal model and human studies of the CNS effects of MDMA and combined MDMA-polydrug toxicity are needed to further explain these findings. Potential explanations for our results including pre-existing brain differences predisposing to MDMA polydrug use, direct MDMA and polydrug toxicity, indirect changes due to MDMA and polydrug toxicity, or combinations of all these factors.

Processing faces and facial expressions

This paper reviews processing of facial identity and expressions. The issue of independence of these two systems for these tasks has been addressed from different approaches over the past 25 years. More recently, neuroimaging techniques have provided researchers with new tools to investigate how facial information is processed in the brain. First, findings from "traditional" approaches to identity and expression processing are summarized. The review then covers findings from neuroimaging studies on face perception, recognition, and encoding. Processing of the basic facial expressions is detailed in light of behavioral and neuroimaging data. Whereas data from experimental and neuropsychological studies support the existence of two systems, the neuroimaging literature yields a less clear picture because it shows considerable overlap in activation patterns in response to the different face-processing tasks. Further, activation patterns in response to facial expressions support the notion of involved neural substrates for processing different facial expressions.

A right hemispheric frontocerebellar network for time discrimination of several hundreds of milliseconds

Debate still surrounds the nature of the role of the dorsolateral prefrontal gyrus (DLPFC) in time perception. This region is frequently associated with working memory and is thus implicated as a so-called "accumulator" within a hypothesized internal clock model. However, we hypothesized that this region may have a more primary role in time perception. To test this hypothesis we used functional magnetic resonance imaging (fMRI) to examine the neural correlates of relatively pure time perception with a temporal discrimination task where intervals of 1 s had to be discriminated from those of 1.3, 1.4, and 1.5 s. Time perception in this particular time domain within the "perceived present" has not previously been investigated using fMRI. By using relatively short time periods to be discriminated and also contrasting activation with an order judgment task, we aimed to minimize the confounding aspects of sustained attention and working memory. In a group of 20 healthy right-handed adult males, neural activation associated with time discrimination was found in a predominantly right hemispheric network of right dorsolateral and inferior prefrontal cortices, right supplementary motor area, and left cerebellum. We conclude that right DLPFC, rather than having a purely working memory function, might be more centrally involved in time perception than previously thought.

LORETA imaging of P300 in schizophrenia with individual MRI and 128-channel EEG

We investigated the characteristics of P300 generators in schizophrenics by using voxel-based statistical parametric mapping of current density images. P300 generators, produced by a rare target tone of 1500 Hz (15%) under a frequent nontarget tone of 1000 Hz (85%), were measured in 20 right-handed schizophrenics and 21 controls. Low-resolution electromagnetic tomography (LORETA), using a realistic head model of the boundary element method based on individual MRI, was applied to the 128-channel EEG. Three-dimensional current density images were reconstructed from the LORETA intensity maps that covered the whole cortical gray matter. Spatial normalization and intensity normalization of the smoothed current density images were used to reduce anatomical variance and subject-specific global activity and statistical parametric mapping (SPM) was applied for the statistical analysis. We found that the sources of P300 were consistently localized at the left superior parietal area in normal subjects, while those of schizophrenics were diversely distributed. Upon statistical comparison, schizophrenics, with globally reduced current densities, showed a significant P300 current density reduction in the left medial temporal area and in the left inferior parietal area, while both left prefrontal and right orbitofrontal areas were relatively activated. The left parietotemporal area was found to correlate negatively with Positive and Negative Syndrome Scale total scores of schizophrenic patients. In conclusion, the reduced and increased areas of current density in schizophrenic patients suggest that the medial temporal and frontal areas contribute to the pathophysiology of schizophrenia, the frontotemporal circuitry abnormality.

Bridging Functional MR Images and Scientific Inference: Reproducibility Maps

Historically, reproducibility has been the sine qua non of experimental findings that are considered to be scientifically useful. Typically, findings from functional magnetic resonance imaging (fMRI) studies are assessed with statistical parametric maps (SPMs) using a p value threshold. However, a smaller p value does not imply that the observed result will be reproducible. In this study, we suggest interpreting SPMs in conjunction with reproducibility evidence. Reproducibility is defined as the extent to which the active status of a voxel remains the same across replicates conducted under the same conditions. We propose a methodology for assessing reproducibility in functional MR images without conducting separate experiments. Our procedures include the empirical Bayes method for estimating effects due to experimental stimuli, the threshold optimization procedure for assigning voxels to the active status, and the construction of reproducibility maps. In an empirical example, we implemented the proposed methodology to construct reproducibility maps based on data from the study by Ishai et al. (2000). The original experiments involved 12 human subjects and investigated brain regions most responsive to visual presentation of 3 categories of objects: faces, houses, and chairs. The brain regions identified included occipital, temporal, and fusiform gyri. Using our reproducibility analysis, we found that subjects in one of the experiments exercised at least 2 mechanisms in responding to visual objects when performing alternately matching and passive tasks. One gave activation maps closer to those reported in Ishai et al., and the other had related regions in the precuneus and posterior cingulate. The patterns of activated regions are reproducible for at least 4 out of 6 subjects involved in the experiment. Empirical application of the proposed methodology suggests that human brains exhibit different strategies to accomplish experimental tasks when responding to stimuli. It is important to correlate activations to subjects' behavior such as reaction time and response accuracy. Also, the latency between the stimulus presentation and the peak of the hemodynamic response function varies considerably among individual subjects according to types of stimuli and experimental tasks. These variations per se also deserve scientific inquiries. We conclude by discussing research directions relevant to reproducibility evidence in fMRI.

Neurocortical electrical activity tomography in chronic schizophrenics

Functional imaging of brain electrical activity was performed in 25 chronic medicated schizophrenics and 40 controls, analyzing the classical frequency bands (delta, theta, alpha, and beta) of 19-channel EEG during resting state to identify brain regions with deviant activity of different functional significances, using LORETA (Low Resolution Tomography) and SPM99 (Statistical Parametric Mapping). Patients differed from controls due to an excess of slow activity comprising delta + theta frequency bands (inhibitory pattern) located at the right middle frontal gyrus, right inferior frontal gyrus, and right insula, as well as at the bilateral anterior cingulum with a left preponderance. The high temporal resolution of EEG enables the specification of the deviations not only as an excess or a deficit of brain electrical activity, but also as inhibitory (delta, theta), normal (alpha), and excitatory (beta) activities. These deviations point out to an impaired functional brain state consisting of inhibited frontal and prefrontal areas that may result in inadequate treatment of externally or internally generated information.

Cerebellar responses evoked by nociceptive leg withdrawal reflex as revealed by event-related FMRI

The aim of the present study was to examine nociceptive leg withdrawal reflex-related areas in the human cerebellum using event-related functional brain imaging (fMRI). Knowledge about cerebellar areas involved in unconditioned limb withdrawal reflex control has some relevance in understanding data of limb withdrawal reflex conditioning studies. Sixteen healthy adult subjects participated. Nociceptive leg withdrawal reflexes were evoked by electrical stimulation of the left tibial nerve behind the medial malleolus. An event-related fMRI paradigm was applied with a total of 30 stimuli being delivered pseudorandomly during 500 consecutive MR scans. Surface electromyographic (EMG) recordings were performed from the left anterior tibial muscle. Only trials with significant reflex EMG activity were used as active events in fMRI statistical analysis. The specified contrasts compared the active event condition with rest. Leg withdrawal reflex-related areas were located within the vermis, paravermis, and lateral posterior cerebellar hemispheres bilaterally. Vermal and paravermal areas in lobules III/IV in the anterior lobe and in lobule VIII in the posterior lobe agree with the cerebellar representation of climbing and mossy fiber hindlimb afferents and voluntary leg movements. They are likely related to efferent modulation of the leg withdrawal reflex and/or sensory processing of afferent inputs from the reflex and/or the noxious stimulus. Additional activation within vermal lobule VI and hemispheral lobules VI/Crus I may be related to other pain-related processes (e.g., facial grimacing, fear, and startlelike reactions).

Lexical decision of nonwords and pseudowords in humans: a positron emission tomography study

In this functional positron emission tomography study brain activations during an auditory lexical decision task with two experimental conditions were investigated. First, the subjects had to discriminate between real words and nonwords; second, real words varied with pseudowords. Comparing each of these tasks to an auditory control condition we found bilateral activation of the superior temporal and inferior frontal gyrus, lateralized to the left in the pseudoword condition. The comparison of the lexical decision tasks revealed higher rCBF during the pseudo-/real word decisions within BA 47, adjacent to Broca's area, and the anterior cingulate. The data support the notion that the lexical decision during a nonword task is mainly based on a phonological discrimination process, whereas a pseudoword task more strongly requires lexical access resulting in activation of BA 47.

fMRI evidence that the neural basis of response inhibition is task-dependent

Event-related fMRI was used to investigate the hypothesis that neural activity involved in response inhibition depends upon the nature of the response being inhibited. Two different Go/No-go tasks were compared-one with a high working memory load and one with low. The 'simple' Go/No-go task with low working memory load required subjects to push a button in response to green spaceships but not red spaceships. A 'counting' Go/No-go task (high working memory load) required subjects to respond to green spaceships as well as to those red spaceships preceded by an even number of green spaceships. In both tasks, stimuli were presented every 1.5 s with a 5:1 ratio of green-to-red spaceships. fMRI group data for each task were analyzed using random effects models to determine signal change patterns associated with Go events and No-go events (corrected P< or =0.05). For both tasks, Go responses were associated with signal change in the left primary sensorimotor cortex, supplementary motor area (SMA) proper, and anterior cerebellum (right>left). For the simple task, No-go events were associated with activation in the pre-SMA; the working memory-loaded 'counting' task elicited additional No-go activation in the right dorsolateral prefrontal cortex. The findings suggest that neural contributions to response inhibition may be task dependent; the pre-SMA appears necessary for inhibition of unwanted movements, while the dorsolateral prefrontal cortex is recruited for tasks involving increased working memory load.

Early 'visual' cortex activation correlates with superior verbal memory performance in the blind

The visual cortex may be more modifiable than previously considered. Using functional magnetic resonance imaging (fMRI) in ten congenitally blind human participants, we found robust occipital activation during a verbal-memory task (in the absence of any sensory input), as well as during verb generation and Braille reading. We also found evidence for reorganization and specialization of the occipital cortex, along the anterior-posterior axis. Whereas anterior regions showed preference for Braille, posterior regions (including V1) showed preference for verbal-memory and verb generation (which both require memory of verbal material). No such occipital activation was found in sighted subjects. This difference between the groups was mirrored by superior performance of the blind in various verbal-memory tasks. Moreover, the magnitude of V1 activation during the verbal-memory condition was highly correlated with the blind individual's abilities in a variety of verbal-memory tests, suggesting that the additional occipital activation may have a functional role.

Brain function and personality in normal males: a SPECT study using statistical parametric mapping

Understanding the differences between individuals' personality types at a functional brain level is now possible due to recent developments in both functional brain imaging and personality models. The psychobiological model for temperament and character offers one approach to exploring personality. This study uses SPECT imaging to investigate brain function in relationship to the personality traits in the Temperament and Character Index. A general linear model approach was implemented at a voxel-by-voxel level, using quartile groupings for the personality predictors. t contrasts were used to investigate significant clusters of activation or deactivation. The results show a number of significant relationships between personality traits and regional cerebral blood flow, which show distinct nonlinear trends. All seven of the Cloninger personality traits were significantly related to regional cerebral blood flow. The results suggest that differences in brain function in some regions may reflect differences in personality traits.

Experimental evaluation of iterative reconstruction versus filtered back projection for 3D [15O]water PET activation studies using statistical parametric mapping analysis

Iterative reconstructions are increasingly used for clinical PET studies owing to the better noise properties compared with filtered backprojection (FBP). The purpose of the present study was to compare ordered subsets expectation maximization (OSEM) iterative reconstruction with FBP as input for statistical parametric mapping (SPM) analysis of PET activation studies. Two phantom studies were performed simulating both motor and cognitive tasks and acquiring data with both high and low statistics. In contrast to clinical studies, where no a priori information is known, phantom studies allow for an accurate and detailed comparison between different reconstruction techniques. The significance of "activations" during "tasks" was determined using SPM99 software. Using region of interest analysis of SPM results, it was found that the maximum and average t values within each hot spot of the phantom were higher for OSEM than for FBP. In addition, OSEM4 x 16 (4 iterations, 16 subsets) produced fewer false-positive voxels than FBP, OSEM1 x 16 and OSEM2 x 16. In conclusion, for PET activation studies use of OSEM4 x 16 seems to give the best tradeoff between signal detection and noise reduction.

Functional MRI using sensitivity-encoded echo planar imaging (SENSE-EPI)

Parallel imaging methods become increasingly available on clinical MR scanners. To investigate the potential of sensitivity-encoded single-shot EPI (SENSE-EPI) for functional MRI, five imaging protocols at different SENSE reduction factors (R) and matrix sizes were compared with respect to their noise characteristics and their sensitivity toward functional activation in a motor task examination. At constant echo times, SENSE-EPI was either used to shorten the single volume acquisition times (TR(min)) at matrix size 128 x 100 (22 slices) from 3.9 s (no SENSE) to 2.0 s at R = 3, or to increase the matrix size to 192 x 153 (22 slices), resulting in TR(min) = 5.3 s for R = 2 or TR(min) = 3.4 s for R = 3. At the lower resolution, the bisection of echo train length (R = 2) substantially reduced distortions and blurring, while signal-to-noise and statistical power (measured by cluster size and maximum t value per unit time) were hardly reduced. At R = 3 the additional gain in speed and distortion reduction was quite small, while signal-to-noise and statistical power dropped significantly. With enhanced spatial resolution the time course signal-to-noise was better than expected from theory for purely thermal noise because of a reduced contribution of physiological noise, and statistical power almost reached that of the regular, low-resolution single-shot EPI, with a slight drop off toward R = 3. Thus, SENSE-EPI allows to substantially increase speed and spatial resolution in fMRI. At SENSE reduction factors up to R = 2, the potential drawbacks regarding signal-to-noise and statistical power are almost negligible.

Tactile-visual cross-modal shape matching: a functional MRI study

The process and location of integration of information from different sensory modalities remains controversial. We used functional MRI to investigate the neural representation of cross-modal matching between tactile and visual shape information in eleven normal volunteers. During the scan, patterns of 2D shapes were presented both tactually and visually, simultaneously. Four different matching tasks were performed: tactile-tactile with eyes closed (TT), tactile-tactile with visual input (TTv), visual-visual with tactile input (VVt), and tactile-visual (TV). The TT task activated the contralateral primary sensorimotor area, and the postcentral gyrus, superior parietal lobules, anterior portion of the intraparietal sulcus, secondary somatosensory cortex, thalamus, dorsal premotor area, cerebellum, and supplementary motor area bilaterally, without occipital involvement. Visual matching activated the primary visual cortex and the lingual and fusiform gyri bilaterally. A cross-modal area was identified by subtracting TTv images from TV images, subtracting VVt images from TV images, and then determining common active areas. There was one discrete area that was active bilaterally; the posterior intraparietal sulcus close to the parieto-occipital sulcus. These data suggest that shape information from different sensory modalities may be integrated in the posterior intraparietal sulcus during tactile-visual matching tasks.

Lactate: a preferred fuel for human brain metabolism in vivo

Recent in vitro studies suggest that lactate, rather than glucose, may be the preferred fuel for neuronal metabolism. The authors examined the effect of lactate on global brain glucose uptake in euglycemic human subjects using 18 fluoro-deoxyglucose (FDG) positron emission tomography (PET). Eight healthy men, aged 40 to 54 years, underwent a 60-minute FDG-PET scan on two occasions in random order. On one occasion, 6.72% sodium lactate was infused at a rate of 50 micro mol. kg-1. min-1 for 20 minutes and then reduced to 30 micro mol. kg-1. min-1; 1.4% sodium bicarbonate was infused as a control on the other occasion. Plasma glucose levels were not different between the two groups (5.3 +/- 0.23 and 5.3 +/- 0.24 mmol/L, P = 0.55). Plasma lactate was significantly elevated by lactate infusion (4.08 +/- 0.35 vs. 0.63 +/- 0.22 mmol/L, P < 0.0005. The whole-brain rate of glucose uptake was significantly reduced by approximately 17% during lactate infusion (0.195 +/- 0.022 vs. 0.234 +/- 0.020 micro mol. g-1. min-1, P = 0.001). The authors conclude that, in vivo in humans, circulating lactate is used by the brain at euglycemia, with sparing of glucose.

A comprehensive study of gray matter loss in patients with Alzheimer's disease using optimized voxel-based morphometry

Voxel-based morphometry (VBM) has already been applied to MRI scans of patients with Alzheimer's disease (AD). The results of these studies demonstrated atrophy of the hippocampus, temporal pole, and insula, but did not describe any global brain changes or atrophy of deep cerebral structures. We propose an optimized VBM method, which accounts for these shortcomings. Additional processing steps are incorporated in the method, to ensure that the whole spectrum of brain atrophy is visualized. A local group template was created to avoid registration bias, morphological opening was performed to eliminate cerebrospinal fluid voxel misclassifications, and volume preserving modulation was used to correct for local volume changes. Group differences were assessed and thresholded at P < 0.05 (corrected). Our results confirm earlier findings, but additionally we demonstrate global cortical atrophy with sparing of the sensorimotor cortex, occipital poles, and cerebellum. Moreover, we show atrophy of the caudate head nuclei and medial thalami. Our findings are in full agreement with the established neuropathological descriptions, offering a comprehensive view of atrophy patterns in AD.

Functional effects of antipsychotic drugs: comparing clozapine with haloperidol

BACKGROUND

Using positron emission tomography (PET) with (15)O water, we compared regional cerebral blood flow (rCBF) patterns induced by clozapine or haloperidol in individuals with schizophrenia. Based on the known clinical characteristics of each drug, we hypothesized that brain regions where the drugs show similar rCBF patterns are among those mediating their antipsychotic actions; whereas, regions where the drugs produce different rCBF patterns are among those mediating their different drug actions, namely, haloperidol's motor side effects or clozapine's unique therapeutic action.

METHODS

Persons with schizophrenia were scanned using PET with (15)O water, first after withdrawal of all psychotropic medication (n = 6), then again after treatment with therapeutic doses of haloperidol (n = 5) or clozapine (n = 5).

RESULTS

Both drugs increased rCBF in the ventral striatum and decreased rCBF in hippocampus and ventrolateral frontal cortex. The rCBF increase associated with haloperidol was greater than that with clozapine in the dorsal and ventral striatum; the rCBF increase with clozapine was greater than that with haloperidol in cortical regions, including anterior cingulate and dorsolateral frontal cortex.

CONCLUSIONS

These data suggest that the rCBF increase in ventral striatum and/or the decrease in hippocampus and/or ventrolateral frontal cortex mediate a common component of antipsychotic action of these drugs. The increased rCBF in dorsal striatum by haloperidol could well be associated with its prominent motor side effects, whereas the increased rCBF in the anterior cingulate or dorsolateral frontal cortex may mediate the superior antipsychotic action of clozapine. The proposals based on these preliminary observations require further study.

Single photon emission computed tomography imaging in obsessive-compulsive disorder and for stereotactic bilateral anterior cingulotomy

In conclusion, the present study suggests that SPECT, using a sophisticated SPM analysis method, may be useful as a potential diagnostic tool for OCD and a possible predictor of treatment outcome for OCD patients undergoing bilateral anterior cingulotomy. The anterior cingulate gyrus seems to be an important structure in the pathogenesis of OCD symptoms. Furthermore, our operative technique of anterior cingulotomy, featuring a larger lesion, seems to be effective in ameliorating the symptoms of OCD without causing any serious complications.

Rapid visuomotor preparation in the human brain: a functional MRI study

An important feature of human motor behaviour is anticipation and preparation. We report a functional magnetic resonance imaging study of the neuronal activation patterns in the human brain that are associated with the rapid visuomotor preparation of discrete finger responses. Our imaging results reveal a large-scale distributed network of neural areas involved in fast visuomotor preparation, including specific areas in the frontal cortex (middle frontal gyrus, premotor and supplementary motor cortex), the parietal cortex (intra-parietal sulcus, inferior and superior parietal lobe) and the basal ganglia. Our reaction time results demonstrate that it is easier to prepare two fingers on one hand than on two hands. This hand-advantage phenomenon was associated with relatively enhanced levels of activity in the basal ganglia and relatively reduced levels of activity in the parietal cortex. These findings provide direct evidence for differential activity in a distributed brain system associated with specific neuro-computational operations subserving fast visuomotor preparation.

A voxel-based morphometry study of temporal lobe gray matter reductions in Alzheimer's disease

Several MRI studies have reported reductions in temporal lobe volumes in Alzheimer's disease (AD). Measures have been usually obtained with regions-of-interest (ROI) drawn manually on selected medial and lateral portions of the temporal lobes, with variable choices of anatomical borders across different studies. We used the fully automated voxel-based morphometry (VBM) approach to investigate gray matter abnormalities over the entire extension of the temporal lobe in 14 AD patients (MMSE 14-25) and 14 healthy controls. Foci of significantly reduced gray matter volume in AD patients were detected in both medial and lateral temporal regions, most significantly in the right and left posterior parahippocampal gyri and the left posterior inferior temporal gyrus/fusiform gyrus (P<0.05, corrected for multiple comparisons). At a more flexible statistical threshold (P<0.001, uncorrected for multiple comparisons), circumscribed foci of significant gray matter reduction were also detected in the right amygdala/enthorinal cortex, the anterior and posterior borders of the superior temporal gyrus bilaterally, and the anterior portion of the left middle temporal gyrus. These VBM results confirm previous findings of temporal lobe atrophic changes in AD, and suggest that these abnormalities may be confined to specific sites within that lobe, rather than showing a widespread distribution.

Dynamics of gray matter loss in Alzheimer's disease

We detected and mapped a dynamically spreading wave of gray matter loss in the brains of patients with Alzheimer's disease (AD). The loss pattern was visualized in four dimensions as it spread over time from temporal and limbic cortices into frontal and occipital brain regions, sparing sensorimotor cortices. The shifting deficits were asymmetric (left hemisphere > right hemisphere) and correlated with progressively declining cognitive status (p < 0.0006). Novel brain mapping methods allowed us to visualize dynamic patterns of atrophy in 52 high-resolution magnetic resonance image scans of 12 patients with AD (age 68.4 +/- 1.9 years) and 14 elderly matched controls (age 71.4 +/- 0.9 years) scanned longitudinally (two scans; interscan interval 2.1 +/- 0.4 years). A cortical pattern matching technique encoded changes in brain shape and tissue distribution across subjects and time. Cortical atrophy occurred in a well defined sequence as the disease progressed, mirroring the sequence of neurofibrillary tangle accumulation observed in cross sections at autopsy. Advancing deficits were visualized as dynamic maps that change over time. Frontal regions, spared early in the disease, showed pervasive deficits later (>15% loss). The maps distinguished different phases of AD and differentiated AD from normal aging. Local gray matter loss rates (5.3 +/- 2.3% per year in AD v 0.9 +/- 0.9% per year in controls) were faster in the left hemisphere (p < 0.029) than the right. Transient barriers to disease progression appeared at limbic/frontal boundaries. This degenerative sequence, observed in vivo as it developed, provides the first quantitative, dynamic visualization of cortical atrophic rates in normal elderly populations and in those with dementia.

Neural correlates of tactile prepulse inhibition: a functional MRI study in normal and schizophrenic subjects

Prepulse inhibition (PPI) of the startle reflex refers to the ability of a weak prestimulus, the prepulse, to inhibit the response to a closely following strong sensory stimulus, the pulse. PPI is found to be deficient in a number of psychiatric and neurological disorders associated with abnormalities at some level in the limbic and cortico-pallido-striato-thalamic circuitry. We applied whole-brain functional magnetic resonance imaging to elucidate the neural correlates of PPI using airpuff stimuli as both the prepulse and the pulse in groups of (i) healthy subjects and (ii) schizophrenic patients. Cerebral activation during prepulse-plus-pulse stimuli with stimulus-onset asynchronies of 120 ms was contrasted with activation during pulse-alone stimuli. In healthy subjects, PPI was associated with increased activation bilaterally in the striatum extending to hippocampus and thalamus, right inferior frontal gyrus and bilateral inferior parietal lobe/supramarginal gyrus, and with decreased activation in the right cerebellum and left medial occipital lobe. All activated regions showed significantly greater response in healthy subjects than schizophrenic patients, who also showed a trend for lower PPI. The findings demonstrate involvement of the striatum, hippocampus, thalamus, and frontal and parietal cortical regions in PPI. Dysfunctions in any of these regions may underlie observations of reduced PPI in schizophrenia.

Regional cerebral blood flow in depressed patients with white matter magnetic resonance hyperintensity

BACKGROUND

Functional neuroimaging studies have consistently demonstrated decreased regional cerebral blood flow (rCBF) or metabolism in the frontal lobe, temporal lobe, or anterior cingulate gyrus of depressed patients. On the other hand, white matter hyperintensity as defined by magnetic resonance imaging (MRI) has been the most consistently replicated finding in structural neuroimaging studies on depression; however, these functional and structural neuroimaging findings of depression have not been well integrated. We aimed to clarify the possible associations of MRI-defined subcortical hyperintensities with rCBF changes in depressed patients.

METHODS

Twelve depressed patients with subcortical hyperintensities defined by MRI, 11 depressed patients without MRI hyperintensities, and 25 healthy volunteers underwent 99mTc ECD SPECT. Group comparisons of their rCBF and correlation analysis between MRI hyperintensity and rCBF in patients were performed with a voxel-based analysis using statistical parametric mapping (SPM) software.

RESULTS

Depressed patients showed decreased rCBF compared with control subjects in the frontal lobe, temporal lobe, and anterior cingulate gyrus whether subcortical hyperintensity existed or not; however, the patients with MRI hyperintensity showed decreased rCBF in the thalamus, basal ganglia, and brainstem in addition to cortical areas. Further, the score for white matter hyperintensity correlated negatively with rCBF in subcortical brain structures, including the thalamus and right basal ganglia.

CONCLUSION

Our study indicates that depressed patients with MRI hyperintensities may have dysfunction in subcortical brain structures in addition to dysfunction in the fronto-temporal cortical structures.