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

The role of immediate and final goals in action planning: An fMRI study

To interact effectively with our environment, we need to specify the intended outcomes (goals) of our actions. In this process, immediate goals and final goals can be regarded as different levels within a hierarchically organized system for action planning: immediate goals and movement details are selected to accomplish more remote goals. Behavioral studies support this notion of different levels of action planning, but the neurophysiological basis remains unclear. Using fMRI, we examined the neural correlates of preparing object manipulations based on either the desired end-state (the final goal) or the initial movement towards a target (the immediate goal). Subjects had to insert an object (consisting of a large and a small cube) into one of two corresponding large and small slots. The subjects were cued on either which slot to fill (Final Goal trials) or which object part to grasp (Immediate Goal trials). These actions required similar movements, but different planning. During Final Goal trials, there was differential preparatory activity along the superior frontal gyrus (bilaterally) and in left inferior parietal cortex. Immediate Goal trials evoked differential activity in occipito-parietal and occipito-temporal cortex. These findings support the notion that actions can be planned at different levels. We show that different fronto-parietal circuits plan the same action, by a relative emphasis on either selecting a sequence of movements to achieve a desired end-state, or selecting movements spatially compatible with given object properties.

Investigation of MCPH1 G37995C and ASPM A44871G polymorphisms and brain size in a healthy cohort

Loss-of-function mutations in MCPH1 and ASPM are responsible for some cases of autosomal recessive primary microcephaly. Recent studies have indicated that certain common variants of these genes have been positively selected for during the evolution of modern humans. It is therefore possible that these variants may predispose to an increase in brain size in the normal human population. We genotyped the MCPH1 G37995C and ASPM A44871G polymorphisms in a cohort of 118 healthy people who had undergone structural magnetic resonance imaging analysis. We did not detect significant association of either MCPH1 G37995C or ASPM A44871G genotype with whole brain volume, cerebral cortical volume or proportion of grey matter in this cohort. Nor did we detect an association of combined MCPH1 37995C and ASPM 44871G allele dosage with these brain measurements. These results were also confirmed in an age-restricted subcohort of 94 individuals. This study suggests that phenotypes other than brain size may have been selected for in ASPM and MCPH1 variants during evolution of modern humans.

Voxel-based investigations of regional cerebral blood flow abnormalities in Alzheimer's disease using a single-detector SPECT system

PURPOSE

To evaluate the feasibility of using the Statistical Parametric Mapping (SPM) program for an automated, voxel-by-voxel assessment of regional cerebral blood flow (rCBF) deficits in Alzheimer's disease (AD) subjects relative to age-matched controls studied with a conventional, single-detector SPECT system.

METHODS

We used a databank of 99mTc-HMPAO images of 19 patients with a diagnosis of probable AD and 15 elderly healthy volunteers; data were acquired using an Orbiter-Siemens single-detector SPECT system. Using SPM, images were transformed spatially, smoothed (12mm), and the data were compared on a voxel-by-voxel basis with t-tests.

RESULTS

There were significant rCBF reductions in AD patients relative to controls involving regions predicted a priori to be affected in AD, namely the left temporal and parietal neocortices, and the right posterior cingulate gyrus (p<0.05, corrected for multiple comparisons).

DISCUSSION

The location of rCBF reductions in AD subjects in our study is consistent with the deficits detected in previous functional imaging studies of AD using higher-resolution devices. This suggests the potential usefulness of using SPM for the analysis of data acquired with single-detector SPECT systems, despite the limited sensitivity and spatial resolution of such equipment.

A single 20 mg dose of the full D1 dopamine agonist dihydrexidine (DAR-0100) increases prefrontal perfusion in schizophrenia

Dopamine D1 receptors play an important role in memory and cognition in non-human primates. Dopamine D1 agonists have been shown to reverse performance deficits in both aged non-human primates and in primates with lesions to dopamine systems. This study explored whether a single dose of the first full D1 agonist dihydrexidine (DAR-0100) would cause changes in brain activity (perfusion) in dopamine-rich brain regions. We used a new gadolinium-contrast magnetic resonance perfusion scanning technique to measure brain activity. A within-subject cross-over double-blind randomized design was used in 20 adults with SCID-diagnosed schizophrenia. Each morning at 0800 h, they were scanned on a 3.0 T MRI scanner for perfusion. They then received either 20 mg of dihydrexidine, or placebo, subcutaneously over 15 min. Over the next 45 min, they had intermittent MRI scans. Two days later, they had a repeat of the Day 1 schedule, but received the opposite treatment from that given on the first day. Within-day, as well as between-day, comparisons were made to test for perfusion effects of dihydrexidine. Analysis revealed that dihydrexidine induced a significant increase in both prefrontal and non-prefrontal perfusion compared to placebo. The greatest increases occurred approximately 20 min after dihydrexidine infusion, consistent with the short pharmacokinetic half-life of dihydrexidine. These data are consistent with the hypothesis formulated from studies of non-human primates that dihydrexidine and other D1 agonists may be able to modulate prefrontal dopaminergic function.

Neural correlates of primary and reflective consciousness of spatial orienting

Using functional magnetic resonance imaging, we asked participants to perform a visual target detection task with peripheral cues. In the first part of the experiment, cues were not predictive of the side of occurrence of the incoming target. In the second part of the experiment, unbeknownst to the participants, cues became 80% predictive, thus inducing an endogenous orienting of spatial attention. Confirming previous results, in the second part response times (RTs) decreased for validly cued trials and increased for invalid trials. Half of the participants were subsequently able to correctly describe the cue-target relationships ('verbalizers'), thus demonstrating reflective consciousness of endogenous orienting. Also non-verbalizer participants showed a similar RT pattern, indicating the occurrence of endogenous orienting without reflective consciousness. Both groups of participants showed fronto-parietal activity typically observed in spatial attention tasks. Verbalizers, in addition, demonstrated stronger activity in the anterior cingulate cortex (ACC), consistent with the proposed role of this structure in purposeful behaviour and in the monitoring of its consequences. The extensive pattern of connectivity of the ACC is ideally suited to integrate the activity of the large neural assemblies necessary for reflective consciousness to emerge.

Accelerated aging of the putamen in men but not in women

Age-related structural brain changes have been demonstrated repeatedly but data on the effect of gender on age-related structural brain changes are conflicting. Using high-resolution T1-weighted magnetic resonance imaging and voxel-based morphometry, we examined a population of 133 healthy adults (women, 73; men, 60; age range, 29-80 years) focusing on differential aging between men and women (i.e., interaction of age and gender). Compared to women, men showed accelerated age-related gray matter (GM) loss in the posterior putamen. Our data may constitute the structural substrate for age-related differences in motor function between men and women such as the higher incidence and earlier onset of Parkinson's disease in men.

Atrophy progression in semantic dementia with asymmetric temporal involvement: a tensor-based morphometry study

We performed a longitudinal anatomical study to map the progression of gray matter atrophy in anatomically defined predominantly left (LTLV) and right (RTLV) temporal lobe variants of semantic dementia (SD). T1-weighted MRI scans were obtained at presentation and one-year follow-up from 13 LTLV, 6 RTLV, and 25 control subjects. Tensor-based morphometry (TBM) in SPM2 was applied to derive a voxel-wise estimation of regional tissue loss over time from the deformation field required to warp the follow-up scan to the presentation scan in each subject. When compared to controls, both LTLV and RTLV showed significant progression of gray matter atrophy not only within the temporal lobe most affected at presentation, but also in the controlateral temporal regions (p<0.05 FWE corrected). In LTLV, significant progression of volume loss also involved the ventromedial frontal and the left anterior insular regions. These results identified the anatomic substrates of the previously reported clinical evolution of LTLV and RTLV into a unique 'merged' clinical syndrome characterized by semantic and behavioral deficits and bilateral temporal atrophy.

Power and sample size calculation for neuroimaging studies by non-central random field theory

Determining power and sample size in neuroimaging studies is a challenging task because of the massive multiple comparisons among tens of thousands of correlated voxels. To facilitate this task, we propose a power analysis method based on random field theory (RFT) by modeling signal areas within images as non-central random field. With this framework, power can be calculated for specific areas of anticipated signals within the brain while accounting for the 3D nature of signals. This framework can also be extended to visualize local variability in sensitivity as a power map and a sample size map. We validated our non-central RFT framework based on Monte-Carlo simulations. Moreover, we applied our method to a blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) data set with a small sample size in order to demonstrate its use in study planning. From the simulations, we found that our method was able to estimate power quite accurately. In the fMRI data analysis, despite the small sample size, we were able to determine power and the number of subjects required to detect signals.

Integrated image- and function-guided surgery in eloquent cortex: a technique report

The ability to effectively identify eloquent cortex in close proximity to brain tumours is a critical component of surgical planning prior to resection. The use of electrocortical stimulation testing (ECS) during awake neurosurgical procedures remains the gold standard for mapping functional areas, yet the preoperative use of non-invasive brain imaging techniques such as fMRI are gaining popularity as supplemental surgical planning tools. In addition, the intraoperative three-dimensional display of fMRI findings co-registered to structural imaging data maximizes the utility of the preoperative mapping for the surgeon. Advances in these techniques have the potential to limit the size and duration of craniotomies as well as the strain placed on the patient, but more research accurately demonstrating their efficacy is required. In this paper, we demonstrate the integration of preoperative fMRI within a neuronavigation system to aid in surgical planning, as well as the integration of these fMRI data with intraoperative ECS mapping results into a three-dimensional dataset for the purpose of cross-validation.

Understanding neuroimaging

Neuroimaging is an emergent method of investigation for studying the human brain in healthy and impaired populations. An increasing number of these investigations involve topics important to rehabilitation. Thus, a basic understanding of the more commonly used neuroimaging techniques is important for understanding and interpreting this growing area of research. Included in this article is a description of the signal source, the advantages and limitations of each technique, considerations for study design, and how to interpret cortical imaging data. Particular emphasis is placed on functional magnetic resonance imaging because of its ubiquitous presence in rehabilitation research.

Bayesian comparison of spatially regularised general linear models

In previous work (Penny et al., [2005]: Neuroimage 24:350-362) we have developed a spatially regularised General Linear Model for the analysis of functional magnetic resonance imaging data that allows for the characterisation of regionally specific effects using Posterior Probability Maps (PPMs). In this paper we show how it also provides an approximation to the model evidence. This is important as it is the basis of Bayesian model comparison and provides a unified framework for Bayesian Analysis of Variance, Cluster of Interest analyses and the principled selection of signal and noise models. We also provide extensions that implement spatial and anatomical regularisation of noise process parameters.

What is Involved and What is Necessary for Complex Linguistic and Nonlinguistic Auditory Processing: Evidence from Functional Magnetic Resonance Imaging and Lesion Data

We used functional magnetic resonance imaging (fMRI) in conjunction with a voxel-based approach to lesion symptom mapping to quantitatively evaluate the similarities and differences between brain areas involved in language and environmental sound comprehension. In general, we found that language and environmental sounds recruit highly overlapping cortical regions, with cross-domain differences being graded rather than absolute. Within language-based regions of interest, we found that in the left hemisphere, language and environmental sound stimuli evoked very similar volumes of activation, whereas in the right hemisphere, there was greater activation for environmental sound stimuli. Finally, lesion symptom maps of aphasic patients based on environmental sounds or linguistic deficits [Saygin, A. P., Dick, F., Wilson, S. W., Dronkers, N. F., & Bates, E. Shared neural resources for processing language and environmental sounds: Evidence from aphasia. Brain, 126, 928–945, 2003] were generally predictive of the extent of blood oxygenation level dependent fMRI activation across these regions for sounds and linguistic stimuli in young healthy subjects.

Pain Enhances Functional Connectivity of a Brain Network Evoked by Performance of a Cognitive Task

Experimental and clinical evidence indicates that pain can affect cognitive processes, but the cortical networks involved in pain-cognition interactions are unclear. In this study, we determined the effect of pain on the activity of cortical areas involved in cognition acting as a whole (i.e., a network). Subjects underwent functional magnetic resonance imaging (fMRI) while engaged in an attention-demanding cognitive task (multisource interference task) of varying difficulty and simultaneously receiving painful stimuli at varying intensities. The control (baseline) condition was simple finger tapping that had minimal cognitive demands and without pain. Functional connectivity analysis revealed a cortical network consisting of two anti-correlated parts: a task-negative part (precuneus/posterior cingulate cortex, medial frontal and inferior parietal/temporal) the activity of which correlated negatively with the cognitive task and positively with the control baseline, and a task-positive part (inferior frontal, superior parietal, premotor, and anterior insula cortices) the activity of which correlated positively with the cognitive task and negatively with the baseline. Independent components analysis revealed these opposing networks were operating at a low frequency (0.03–0.08 Hz). The functional connectivity of the task-positive network was increased by cognitive demand and by pain. We suggest this attention-specific network balances the needs of general self-referential and environmental awareness versus focused attention to salient information. We postulate that pain affects cognitive ability by its reliance on this common attention-specific network. These data provide evidence that pain can modulate a network presumed to be involved in focused attention, suggesting a mechanism for the interference of pain on cognitive ability by the consumption of attentional resources.

Dense mode clustering in brain maps

A mode-based clustering method is developed for identifying spatially dense clusters in brain maps. This type of clustering focuses on identifying clusters in brain maps independent of their shape or overall variance. This can be useful for both localization in terms of interpretation and for subsequent graphical analysis that might require more coherent or dense regions of interest as starting points. The method automatically does signal/noise sharpening through density mode seeking. We also discuss the problem of parameter selection with this method and propose a new method involving 2-parameter control surface, in which we show that the same cluster solution results from tradeoff of these 2 parameters (the local density k and the radius r of the spherical kernel). We benchmark the new dense mode clustering by using several artificially created data sets and brain imaging data sets from an event perception task by perturbing the data set with noise and measuring three kinds of deviation from the original cluster solution. We present benchmark results that demonstrate that the mode clustering method consistently outperforms the commonly used single-linkage clustering, k means method (centroid method) and Ward's method (variance method).

Nonparametric statistical testing of EEG- and MEG-data

In this paper, we show how ElectroEncephaloGraphic (EEG) and MagnetoEncephaloGraphic (MEG) data can be analyzed statistically using nonparametric techniques. Nonparametric statistical tests offer complete freedom to the user with respect to the test statistic by means of which the experimental conditions are compared. This freedom provides a straightforward way to solve the multiple comparisons problem (MCP) and it allows to incorporate biophysically motivated constraints in the test statistic, which may drastically increase the sensitivity of the statistical test. The paper is written for two audiences: (1) empirical neuroscientists looking for the most appropriate data analysis method, and (2) methodologists interested in the theoretical concepts behind nonparametric statistical tests. For the empirical neuroscientist, a large part of the paper is written in a tutorial-like fashion, enabling neuroscientists to construct their own statistical test, maximizing the sensitivity to the expected effect. And for the methodologist, it is explained why the nonparametric test is formally correct. This means that we formulate a null hypothesis (identical probability distribution in the different experimental conditions) and show that the nonparametric test controls the false alarm rate under this null hypothesis.

Diffusion tensor imaging of the corpus callosum: a cross-sectional study across the lifespan

Previous studies have demonstrated strong developmental trends of white matter using in vivo neuroimaging. However, few studies have examined white matter using diffusion tensor imaging across the lifespan. In the present study we examined fractional anisotropy and volume in the corpus callosum in four groups (children, adolescents, young adults, and elderly). Results revealed a curvilinear relationship in the analysis of the fractional anisotropy values for these four groups, with fractional anisotropy values increasing in childhood and adolescence, reaching their peak in young adulthood, followed by a non-significant decline in the elderly. Volumetric analysis of corpus callosum regions revealed a similar pattern, with an increase in volume from childhood and adolescence through young adulthood, and a non-significant decrease in volume in the elderly group. These results define the microstructural development of the white matter across the lifespan. Future studies are required to examine the neurobehavioral correlates of these neuroimaging indices.

Volitional control of attention and brain activation in dual task performance

This study used functional MRI (fMRI) to examine the neural effects of willfully allocating one's attention to one of two ongoing tasks. In a dual task paradigm, participants were instructed to focus either on auditory sentence comprehension, mental rotation, or both. One of the major findings is that the distribution of brain activation was amenable to strategic control, such that the amount of activation per task was systematically related to the attention-dividing instructions. The activation in language processing regions was lower when attending to mental rotation than when attending to the sentences, and the activation in visuospatial processing regions was lower when attending to sentences than when attending to mental rotations. Additionally, the activation was found to be underadditive, with the dual-task condition eliciting less activation than the sum of the attend sentence and attend rotation conditions. We also observed a laterality shift across conditions within language-processing regions, with the attend sentence condition showing bilateral activation, while the dual task condition showed a left hemispheric dominance. This shift suggests multiple language-processing modes and may explain the underadditivity in activation observed in the current and previous studies.

A magnetic resonance imaging study of patients with Parkinson's disease with mild cognitive impairment and dementia using voxel-based morphometry

BACKGROUND

Dementia is common in Parkinson's disease, but the underlying brain pathology is not yet fully understood.

AIM

To examine the changes in the brain of patients with Parkinson's disease with mild cognitive impairment (MCI) and dementia, using structural magnetic resonance imaging.

METHODS

Using voxel-based morphometry, the grey matter atrophy on brain images of patients with Parkinson's disease and dementia (PDD; n = 16) and Parkinson's disease without dementia (PDND; n = 20), and healthy elderly subjects (n = 20) was studied. In the PDND group, 12 subjects had normal cognitive status and 8 had MCI. Standardised rating scales for motor, cognitive and psychiatric symptoms were used.

RESULTS

Widespread areas of cortical atrophy were found in patients with PDD compared with normal controls (in both temporal and frontal lobes and in the left parietal lobe). Grey matter reductions were found in frontal, parietal, limbic and temporal lobes in patients with PDD compared with those with PDND. In patients with PDND with MCI, areas of reduced grey matter in the left frontal and both temporal lobes were found.

CONCLUSION

These findings show that dementia in Parkinson's disease is associated with structural neocortical changes in the brain, and that cognitive impairment in patients with PDND may be associated with structural changes in the brain. Further studies with larger groups of patients are needed to confirm these findings.

Attention alters neural responses to evocative faces in behaviorally inhibited adolescents

Behavioral inhibition (BI) is a risk factor for anxiety disorders. While the two constructs bear behavioral similarities, previous work has not extended these parallels to the neural level. This study examined amygdala reactivity during a task previously used with clinically anxious adolescents. Adolescents were selected for enduring patterns of BI or non-inhibition (BN). We examined amygdala response to evocative emotion faces in BI (N=10, mean 12.8 years) and BN (N=17, mean 12.5 years) adolescents while systematically manipulating attention. Analyses focused on amygdala response during subjective ratings of internal fear (constrained attention) and passive viewing (unconstrained attention) during the presentation of emotion faces (Happy, Angry, Fearful, and Neutral). BI adolescents, relative to BN adolescents, showed exaggerated amygdala response during subjective fear ratings and deactivation during passive viewing, across all emotion faces. In addition, the BI group showed an abnormally high amygdala response to a task condition marked by novelty and uncertainty (i.e., rating fear state to a Happy face). Perturbations in amygdala function are evident in adolescents temperamentally at risk for anxiety. Attention state alters the underlying pattern of neural processing, potentially mediating the observed behavioral patterns across development. BI adolescents also show a heightened sensitivity to novelty and uncertainty, which has been linked to anxiety. These patterns of reactivity may help sustain early temperamental biases over time and contribute to the observed relation between BI and anxiety.

Altered effective connectivity within the language network in primary progressive aphasia

Primary progressive aphasia (PPA) is a neurodegenerative dementia syndrome principally characterized by the gradual dissolution of language functions, especially in the early stages of disorder. In a previous functional neuroimaging study, PPA patients were found to activate core language areas similarly to control subjects when performing semantic and phonological processing tasks (Sonty et al., 2003). In the present study, functional magnetic resonance imaging (fMRI) and dynamic causal modeling (DCM) were used to study multiregional effective connectivity in early-stage PPA (n = 8) and control (n = 8) subjects performing semantic word matching and visual letter matching tasks. fMRI analysis showed semantic task-specific activations in the left inferior frontal (Broca's area) and posterior superior temporal (Wernicke's area) regions, in addition to other language regions, in both groups. Using a model language network consisting of six left hemisphere regions, the DCM analysis demonstrated reduced language-specific effective connectivity between Wernicke's and Broca's areas in the PPA patient group. Furthermore, this decrement in connectivity was predictive of semantic task accuracy. These results demonstrate for the first time that dysfunctional network interactions (effective connectivity), rather than hypoactivity within individual brain regions, may contribute to the emergence of language deficits seen in PPA.

Insight and regional brain volumes in schizophrenia

We have investigated the relationship between insight impairment and regional brain volumes (gray and white matter) in schizophrenia using voxel-based morphometry (VBM). Fifty patients with schizophrenia were evaluated using the Scale for Unawareness of Mental Disorders. Magnetic resonance images were acquired, segmented and spatially normalized using optimized VBM routines. No significant inverse correlations were detected between insight impairment and gray or white matter volumes in the prefrontal region (where significant findings had been predicted a priori), or in any other brain areas. Our results do not support previous hypotheses suggesting a relationship between frontal lobe atrophy and impaired insight in patients with schizophrenia.

Prospective reports of chronic life stress predict decreased grey matter volume in the hippocampus

Chronic stress in non-human animals decreases the volume of the hippocampus, a brain region that supports learning and memory and that regulates neuroendocrine activity. In humans with stress-related psychiatric syndromes characterized by impaired learning and memory and dysregulated neuroendocrine activity, surrogate and retrospective indicators of chronic stress are also associated with decreased hippocampal volume. However, it is unknown whether chronic stress is associated with decreased hippocampal volume in those without a clinical syndrome. We tested whether reports of life stress obtained prospectively over an approximate 20-year period predicted later hippocampal grey matter volume in 48 healthy postmenopausal women. Women completed the Perceived Stress Scale repeatedly from 1985 to 2004; in 2005 and 2006, their hippocampal grey matter volume was quantified by voxel-based morphometry. Higher Perceived Stress Scale scores from 1985 to 2004 - an indicator of more chronic life stress - predicted decreased grey matter volume in the right orbitofrontal cortex and right hippocampus. These relationships persisted after accounting for age, total grey matter volume, time since menopause, use of hormone therapy, subclinical depressive symptoms, and other potentially confounding behavioral and age-related cerebrovascular risk factors. The relationship between chronic life stress and regional grey matter volume - particularly in the hippocampus and orbitofrontal cortex - appears to span a continuum that extends to otherwise healthy individuals. Consistent with animal and human clinical evidence, we speculate that chronic-stress-related variations in brain morphology are reciprocally and functionally related to adaptive and maladaptive changes in cognition, neuroendocrine activity, and psychiatric vulnerability.

Smaller regional volumes of brain gray and white matter demonstrated in breast cancer survivors exposed to adjuvant chemotherapy

BACKGROUND

Previous studies have shown cognitive impairment in breast cancer survivors who were exposed to adjuvant chemotherapy. Neural damage by chemotherapy might have played some part in these findings. The current study explored the regional brain volume difference between breast cancer survivors exposed to adjuvant chemotherapy (C+) and those unexposed (C-).

METHODS

High-resolution 1.5-tesla brain magnetic resonance imaging (MRI) databases of breast cancer survivors and healthy controls were used. Brain images were preprocessed for optimal voxel-based morphometry. Comparisons of gray matter and white matter were performed between the C+ and the C- groups, by using MRI scans from within 1 year (the 1-year study, n = 51 and n = 55, respectively) or 3 years after their cancer surgery (the 3-year study, n = 73 and n = 59, respectively). As exploratory analyses, correlation analyses were performed between indices of the Wechsler Memory Scale-Revised and regional brain volume where the volume were significantly smaller. As a reference, MRI scans of cancer survivors were compared with those of healthy controls (n = 55 for the 1-year study and n = 37 for the 3-year study).

RESULTS

The C+ patients had smaller gray matter and white matter including prefrontal, parahippocampal, and cingulate gyrus, and precuneus in the 1-year study. However, no difference was observed in the 3-year study. The volumes of the prefrontal, parahippocampal gyrus, and precuneus were significantly correlated with indices of attention/concentration and/or visual memory. Comparisons with healthy controls did not show any significant differences.

CONCLUSIONS

Adjuvant chemotherapy might have an influence on brain structure, which may account for previously observed cognitive impairments.

An fMRI study of somatosensory-implicated acupuncture points in stable somatosensory stroke patients

PURPOSE

To assess differences in brain responses between stroke patients and controls to tactile and electrical acupuncture stimulation using functional MRI (fMRI).

MATERIALS AND METHODS

A total of 12 male, clinically stable stroke patients with left side somatosensory deficits, and 12 age-matched male control subjects were studied. fMRI was performed with two different paradigms; namely, tactile stimuli and electrical stimulation at acupuncture points LI4 and LI11 on the affected side of the body. fMRI data were analyzed using SPM99.

RESULTS

Tactile stimulation in both patients and controls produced significant activation in primary and secondary sensory and motor cortical areas and cerebellum. Greater activation was present in patients than controls in the somatosensory cortex with both the tactile task and the acupuncture point (acupoint) stimulation. Activation was greater during the tactile task than the acupuncture stimulation in patients and normal controls.

CONCLUSION

Differences observed between patients and controls on both tasks may indicate compensatory over recruitment of neocortical areas involved in somatosensory perception in the stroke patients. The observed differences between patients and controls on the acupoint stimulation task may also indicate that stimulation of acupoints used therapeutically to enhance recovery from stroke, selectively activates areas thought to be involved in mediating recovery from stroke via functional plasticity. fMRI of acupoint stimulation may illustrate the functional substrate of the therapeutically beneficial effect of acupuncture in stroke rehabilitation.

Probing the neural correlates of associative memory formation: a parametrically analyzed event-related functional MRI study

The medial temporal lobe (MTL) is crucial for declarative memory formation, but the function of its subcomponents in associative memory formation remains controversial. Most functional imaging studies on this topic are based on a stepwise approach comparing a condition with and one without associative encoding. Extending this approach we applied additionally a parametric analysis by varying the amount of associative memory formation. We found a hippocampal subsequent memory effect of almost similar magnitude regardless of the amount of associations formed. By contrast, subsequent memory effects in rhinal and parahippocampal cortices were parametrically and positively modulated by the amount of associations formed. Our results indicate that the parahippocampal region supports associative memory formation as tested here and the hippocampus adds a general mnemonic operation. This pattern of results might suggest a new interpretation. Instead of having either a fixed division of labor between the hippocampus (associative memory formation) and the rhinal cortex (non-associative memory formation) or a functionally unitary MTL system, in which all substructures are contributing to memory formation in a similar way, we propose that the location where associations are formed within the MTL depends on the kind of associations bound: If visual single-dimension associations, as used here, can already be integrated within the parahippocampal region, the hippocampus might add a general purpose mnemonic operation only. In contrast, if associations have to be formed across widely distributed neocortical representations, the hippocampus may provide a binding operation in order to establish a coherent memory.

Striatal gray matter loss in Huntington's disease is leftward biased

In Huntington's disease (HD), the distribution of pathological changes throughout the brain is incompletely understood. Some studies have identified leftward-biased lateralization, whereas others did not. We performed magnetic resonance imaging and a voxel-based asymmetry analysis in 44 right-handed HD gene carriers (presymptomatic, n = 5; stage I, n = 28; stage II, n = 11) and 44 right-handed healthy controls. The group comparison revealed leftward-biased gray matter loss in the striatum. Further analyses showed no indication of asymmetry in presymptomatic HD patients but an increase in asymmetry in the course of the HD stages under examination. Our study demonstrates and discusses leftward-biased gray matter loss in HD.

Non-rigid alignment of pre-operative MRI, fMRI, and DT-MRI with intra-operative MRI for enhanced visualization and navigation in image-guided neurosurgery

OBJECTIVE

The usefulness of neurosurgical navigation with current visualizations is seriously compromised by brain shift, which inevitably occurs during the course of the operation, significantly degrading the precise alignment between the pre-operative MR data and the intra-operative shape of the brain. Our objectives were (i) to evaluate the feasibility of non-rigid registration that compensates for the brain deformations within the time constraints imposed by neurosurgery, and (ii) to create augmented reality visualizations of critical structural and functional brain regions during neurosurgery using pre-operatively acquired fMRI and DT-MRI.

MATERIALS AND METHODS

Eleven consecutive patients with supratentorial gliomas were included in our study. All underwent surgery at our intra-operative MR imaging-guided therapy facility and have tumors in eloquent brain areas (e.g. precentral gyrus and cortico-spinal tract). Functional MRI and DT-MRI, together with MPRAGE and T2w structural MRI were acquired at 3 T prior to surgery. SPGR and T2w images were acquired with a 0.5 T magnet during each procedure. Quantitative assessment of the alignment accuracy was carried out and compared with current state-of-the-art systems based only on rigid registration.

RESULTS

Alignment between pre-operative and intra-operative datasets was successfully carried out during surgery for all patients. Overall, the mean residual displacement remaining after non-rigid registration was 1.82 mm. There is a statistically significant improvement in alignment accuracy utilizing our non-rigid registration in comparison to the currently used technology (p<0.001).

CONCLUSIONS

We were able to achieve intra-operative rigid and non-rigid registration of (1) pre-operative structural MRI with intra-operative T1w MRI; (2) pre-operative fMRI with intra-operative T1w MRI, and (3) pre-operative DT-MRI with intra-operative T1w MRI. The registration algorithms as implemented were sufficiently robust and rapid to meet the hard real-time constraints of intra-operative surgical decision making. The validation experiments demonstrate that we can accurately compensate for the deformation of the brain and thus can construct an augmented reality visualization to aid the surgeon.

Cerebrocerebellar circuits for the perceptual cancellation of eye-movement-induced retinal image motion

Despite smooth pursuit eye movements, we are unaware of resultant retinal image motion. This example of perceptual invariance is achieved by comparing retinal image slip with an internal reference signal predicting the sensory consequences of the eye movement. This prediction can be manipulated experimentally, allowing one to vary the amount of self-induced image motion for which the reference signal compensates and, accordingly, the resulting percept of motion. Here we were able to map regions in CRUS I within the lateral cerebellar hemispheres that exhibited a significant correlation between functional magnetic resonance imaging signal amplitudes and the amount of motion predicted by the reference signal. The fact that these cerebellar regions were found to be functionally coupled with the left parieto-insular cortex and the supplementary eye fields points to these cortical areas as the sites of interaction between predicted and experienced sensory events, ultimately giving rise to the perception of a stable world despite self-induced retinal motion.

Reciprocal Benefits of Mass-Univariate and Multivariate Modeling in Brain Mapping: Applications to Event-Related Functional MRI, H(2) (15)O-, and FDG-PET

In brain mapping studies of sensory, cognitive, and motor operations, specific waveforms of dynamic neural activity are predicted based on theoretical models of human information processing. For example in event-related functional MRI (fMRI), the general linear model (GLM) is employed in mass-univariate analyses to identify the regions whose dynamic activity closely matches the expected waveforms. By comparison multivariate analyses based on PCA or ICA provide greater flexibility in detecting spatiotemporal properties of experimental data that may strongly support alternative neuroscientific explanations. We investigated conjoint multivariate and mass-univariate analyses that combine the capabilities to (1) verify activation of neural machinery we already understand and (2) discover reliable signatures of new neural machinery. We examined combinations of GLM and PCA that recover latent neural signals (waveforms and footprints) with greater accuracy than either method alone. Comparative results are illustrated with analyses of real fMRI data, adding to Monte Carlo simulation support.

Practice makes perfect: the neural substrates of tactile discrimination by Mah-Jong experts include the primary visual cortex

BACKGROUND

It has yet to be determined whether visual-tactile cross-modal plasticity due to visual deprivation, particularly in the primary visual cortex (V1), is solely due to visual deprivation or if it is a result of long-term tactile training. Here we conducted an fMRI study with normally-sighted participants who had undergone long-term training on the tactile shape discrimination of the two dimensional (2D) shapes on Mah-Jong tiles (Mah-Jong experts). Eight Mah-Jong experts and twelve healthy volunteers who were naïve to Mah-Jong performed a tactile shape matching task using Mah-Jong tiles with no visual input. Furthermore, seven out of eight experts performed a tactile shape matching task with unfamiliar 2D Braille characters.

RESULTS

When participants performed tactile discrimination of Mah-Jong tiles, the left lateral occipital cortex (LO) and V1 were activated in the well-trained subjects. In the naïve subjects, the LO was activated but V1 was not activated. Both the LO and V1 of the well-trained subjects were activated during Braille tactile discrimination tasks.

CONCLUSION

The activation of V1 in subjects trained in tactile discrimination may represent altered cross-modal responses as a result of long-term training.

Neural substrates of sarcasm: a functional magnetic-resonance imaging study

The understanding of sarcasm reflects a complex process, which involves recognizing the beliefs of the speaker. There is a clear association between deficits in mentalizing, which is the ability to understand other people's behavior in terms of their mental state, and the understanding of sarcasm in individuals with autistic spectrum disorders. This suggests that mentalizing is important in pragmatic non-literal language comprehension. To highlight the neural substrates of sarcasm, 20 normal adult volunteers underwent functional magnetic-resonance imaging. We used scenario-reading tasks, in which sentences describing a certain situation were presented, followed by the protagonist's comments regarding that situation. Depending on the situation, the semantic content of the comments was classified as sarcastic, non-sarcastic, or contextually unconnected. As the combination of the first and second sentences represented discourse-level information that was not encoded in the individual sentences, sarcasm detection was represented as the differential activation induced by the second sentences. Sarcasm detection activated the left temporal pole, the superior temporal sulcus, the medial prefrontal cortex, and the inferior frontal gyrus (Brodmann's area [BA] 47). The left BA 47 was activated more prominently by sarcasm detection than by the first sentence. These findings indicate that the detection of sarcasm recruits the medial prefrontal cortex, which is part of the mentalizing system, as well as the neural substrates involved in reading sentences. The left BA 47 might therefore be where mentalizing and language processes interact during sarcasm detection.

Medial frontal cortex perfusion abnormalities as evaluated by positron emission tomography in women with climacteric symptoms

OBJECTIVE

To identify functional changes in the brains of women with climacteric symptoms. Images of regional cerebral blood flow (rCBF) were compared statistically between women with and women without symptoms to identify changes in rCBF. Results may provide a better understanding of the neural basis of the symptoms, which are divided into three symptom clusters: vasomotor, psychological, and somatic.

DESIGN

The study participants consisted of 12 women with moderate to severe climacteric symptoms (age 47.5 +/- 5.9 years, mean +/- SD) and 7 women with no symptoms (control group; age 49.6 +/- 4.2 years, mean +/- SD). The study participants were patients at a menopause clinic, and the latter were healthy volunteer nurses and hospital staff. Climacteric symptoms were evaluated by an assessment of the severity of 17 symptoms immediately before positron emission tomography examination of rCBF. The symptoms had been used previously to generate the Kupperman Kohnenki Shogai Index, a modified Kupperman Menopausal Index adapted to Japanese women. rCBF was measured by positron emission tomography with the CO2 dynamic inhalation method.

RESULTS

Reductions in relative rCBF in the patient group were observed in the bilateral rectal gyrus and in the left subcallosal gyrus on a voxel-by-voxel basis as compared with the control group.

CONCLUSIONS

The present study revealed reductions in relative rCBF of the prefrontal cortex of Japanese women with moderate to severe climacteric symptoms. This area is close to that previously addressed in studies of familial bipolar depression and familial unipolar depression, although our participants did not satisfy criteria for depression. This reduction of rCBF may be related to the three climacteric symptom clusters, but further studies are needed for evaluation of its significance. Our results should stimulate investigations into the positron emission tomography rCBF change of these women as to the integration of multiple entities in climacteric symptoms.

Correlation between changes in regional cerebral blood flow and pain relief in complex regional pain syndrome type 1

OBJECTIVE

Analyzing changes in regional cerebral blood flow (rCBF) with SPECT in complex regional pain syndrome type 1 (CRPS 1), formerly known as reflex sympathetic dystrophy, is an optimal method for evaluating effective pain relief. We attempted to investigate the correlation of changes in rCBF with pain relief during treatments of sympathetic blockade and multimodal epidural pain control.

CASE REPORT

We describe a patient with severe CRPS 1 in whom conventional treatment failed to relieve the pain. Combined repeated lumbar sympathetic blocks and long-term epidural morphine, bupivacaine, and ketamine administration provided satisfactory pain relief and functional activity recovery. Six normal control subjects having one Tc-99m HMPAO scan each and the patient with CRPS having 3 Tc-99m HMPAO scans (once before treatment and twice at 4 months and 6 months after treatment, respectively). The patient with CRPS showed lower rCBF than normal controls in the left thalamus and higher rCBF than normal controls in the right parietal lobe and left frontal lobe. After subsequent treatment, the subtraction images showed increased rCBF in the left thalamus and decreased rCBF in the right parietal and left frontal lobes.

CONCLUSIONS

Tc-99m HMPAO SPECT showed a relationship of rCBF in the thalamus, parietal lobe, and frontal lobe with pain relief. rCBF alterations may provide an indicator for the quality of pain management for neuropathic pains. Subtraction analysis between pre- and posttreatment, by using statistical parametric mapping (version 2), can be used as an objective indicator for the effectiveness of therapy.

Topography of Cortical Activation Differs for Fundamental and Harmonic Frequencies of the Steady-State Visual-Evoked Responses. An EEG and PET H215O Study

In humans, visual flicker stimuli of graded frequency (2-90 Hz) elicit an electroencephalographic (EEG) steady-state visual-evoked response (SSVER) with the same fundamental frequency as the stimulus and, in addition, a series of harmonic responses. The fundamental component of the SSVER is generated by increased synaptic activity in primary visual cortex (V1). We set out to determine the cortical origin of the harmonic responses in humans. For this purpose, we recorded the SSVERs at 5 different frequencies (5, 10, 15, 25, and 40 Hz) and measured regional cerebral blood flow (rCBF) with positron emission tomography-H(2)(15)O at rest and during visual stimulation at the same frequencies. The rCBF contrast weighted by the amplitude of the SSVERs first harmonics showed activation of a swath of cortex perpendicular to V1, including mostly the inferior half of the parieto-occipital sulcus. This area overlapped minimally with the primary visual cortex activated by the fundamental frequency. A different method, estimating EEG cortical source current density with low-resolution brain electromagnetic tomography, gave the same results. Our finding suggests that the inferior portion of the banks of the parieto-occipital sulci contains association visual cortex involved in the processing of stimuli that can be as simple as a flickering light source.

Voxel-based morphometry indicates relative preservation of the limbic prefrontal cortex in early Huntington disease

In Huntington disease (HD), both the genetic defect and mutant gene product huntington are known but the exact mechanisms that lead to neuronal loss are poorly understood. Until now, the distribution of tissue loss throughout the brain has been investigated intensively. Here we searched for areas that, antipodal to the striatum, display grey-matter (GM) preservation. We performed high resolution T1-weighted magnetic resonance imaging and voxel-based morphometry in 46 patients in early HD and 46 healthy controls. We applied an analysis of covariance (ANCOVA) model with the total GM volume of each participant as covariate. In accordance with earlier reports, group comparisons revealed GM decrease in the striatum, insula, and thalamus as well as in dorsolateral frontal and occipital areas. In contrast, the limbic prefrontal cortex displayed GM preservation. Our findings support hypotheses that postulate differential involvement of frontosubcortical circuits in the pathophysiology of HD.

The relationship between frontal gray matter volume and cognition varies across the healthy adult lifespan

OBJECTIVE

Age-associated decline in gray matter brain volume and cognitive function in healthy adults has been reported in the literature. The goal of the current study is to examine the relationship between age-related changes in regional gray matter volumes and cognitive function in a large, cross-sectional sample of healthy adults across the lifespan.

METHODS

Magnetic resonance imaging and cognitive assessment were conducted on 148 adults aged 21-76 years. Multiple regression analyses examining the effect of age were performed on magnetic resonance image-derived gray matter brain volumes and standardized cognitive summary scores of attention and executive function. Regression was also performed to test the effect of age, gray matter volumes, and their interaction on the prediction of cognitive performance.

RESULTS

Age significantly predicted performance on tests of attention (F [1, 146]=50.97, p <0.01, R2=0.26) and executive function (F [1, 146]=126.19, p <0.01, R2=0.46) and gray matter volumes for frontal subregions (lateral, medial, orbital), hippocampus, amygdala, and putamen (F [2, 145]=45.34-23.96, p <0.01-0.02). Lateral frontal (beta=-1.53, t=-2.16, df=131, p <0.03) and orbital frontal (beta=1.24, t=2.08, df=131, p <0.04) regions significantly predicted performance on tests of attention. Lateral frontal (beta=-1.69, t=-2.83, df=131, p <0.01) and the interaction between age and lateral frontal volume (beta=3.76, t=2.49, df=131, p <0.02) significantly predicted executive function.

CONCLUSIONS

The findings confirm age-associated decline in cognitive function and gray matter volumes, particularly in anterior cortical brain regions. Furthermore, the association between lateral frontal gray matter volume and the ability to successfully plan, organize, and execute strategies varies as a function of age across the healthy adult lifespan.

Structural neuroimaging research methods in geriatric depression

Geriatric depression consists of complex and heterogeneous behaviors unlikely to be caused by a single brain lesion. However, there is evidence that abnormalities in specific brain structures and their interconnections confer vulnerability to the development of late-life depression. Structural magnetic resonance imaging methods can be used to identify and quantify brain abnormalities predisposing to geriatric depression and in prediction of treatment response. This article reviews several techniques, including morphometric approaches, study of white matter hyperintensities, diffusion tensor imaging, magnetization transfer imaging, t2 relaxography, and spectroscopy, that have been used to examine these brain abnormalities with a focus on the type of information obtained by each method as well as each method's limitations. The authors argue that the available methods provide complementary information and that, when combined judiciously, can increase the knowledge gained from neuroimaging findings and conceptually advance the field of geriatric depression.

The right hippocampus participates in short-term memory maintenance of object–location associations

Doubts have been cast on the strict dissociation between short- and long-term memory systems. Specifically, several neuroimaging studies have shown that the medial temporal lobe, a region almost invariably associated with long-term memory, is involved in active short-term memory maintenance. Furthermore, a recent study in hippocampally lesioned patients has shown that the hippocampus is critically involved in associating objects and their locations, even when the delay period lasts only 8 s. However, the critical feature that causes the medial temporal lobe, and in particular the hippocampus, to participate in active maintenance is still unknown. This study was designed in order to explore hippocampal involvement in active maintenance of spatial and non-spatial associations. Eighteen participants performed a delayed-match-to-sample task in which they had to maintain either object-location associations, color-number association, single colors, or single locations. Whole-brain activity was measured using event-related functional magnetic resonance imaging and analyzed using a random effects model. Right lateralized hippocampal activity was evident when participants had to maintain object-location associations, but not when they had to maintain object-color associations or single items. The present results suggest a hippocampal involvement in active maintenance when feature combinations that include spatial information have to be maintained online.

Structural correlates of intellectual impairment and autistic features in adolescents

Intellectual disability, a common but under-researched condition, is strongly associated with autism spectrum disorders (ASD). Although studies have investigated the neural correlates of intelligence quotient (IQ) and ASD in intellectually unimpaired subjects, these issues have not been addressed in intellectually impaired subjects. We studied 63 intellectually disabled adolescents receiving additional learning support and 72 controls using whole brain tissue volumes extracted from native space and voxel-based morphometry (VBM) in normalised space. We applied a qualitative and quantitative review of VBM preprocessing and modified the optimised method to establish optimum co-registration of the brains in normalised space. We report tissue density differences at cluster level with adjustment for underlying smoothness. Individuals with intellectual disability had smaller total white matter and total brain tissue volumes than controls, as well as reduced grey matter density in the right cerebellar hemisphere and left temporo-parietal cortex, and reduced white matter density in the posterior corpus callosum. Intellectually disabled subjects were additionally subgrouped according to their degree of reported autistic features. Reduced grey matter density was detected in the thalamus of subjects with autistic features scoring within the pervasive developmental disorder range as compared to subjects below the threshold for ASD, and increased white matter density was detected in the left superior temporal gyrus of subjects scoring above the threshold for autism as compared to subjects below the threshold for ASD.

Bilateral grey-matter increase in the putamen in primary blepharospasm

BACKGROUND

Primary blepharospasm is a focal dystonia characterised by excessive involuntary closure of the eyelids. The pathophysiology of primary blepharospasm is unresolved.

AIM

To pinpoint grey-matter changes that are associated with primary blepharospasm.

METHODS

16 right-handed patients with primary blepharospasm (mean age 67.4 (SD 4.3) years; 12 women) were compared with 16 healthy volunteers matched for sex and age. High-resolution T1-weighted magnetic resonance imaging of each participant was obtained and analysed by voxel-based morphometry, a method to detect regionally specific differences in grey matter between patients and control group. To evaluate whether the identified grey-matter changes were correlated with the duration of primary blepharospasm or botulinum neurotoxin treatment (BoNT), separate regression analyses were carried out.

RESULTS

In patients with primary blepharospasm, grey-matter increase in the putamina was observed, whereas regression analyses did not indicate a correlation between grey-matter increases and the duration of primary blepharospasm or BoNT. Grey-matter decrease was detected in the left inferior parietal lobule; here regression analyses of grey-matter decrease showed a significant (p = 0.013) correlation of grey-matter decrease with the duration of BoNT.

CONCLUSIONS

The data suggest structural changes in primary blepharospasm and point to a crucial role of the putamen for the pathophysiology of this focal dystonia.

Regional white matter and neuropsychological functioning across the adult lifespan

BACKGROUND

The current study utilized magnetic resonance imaging (MRI) to more fully elucidate the relationship among age, regional white matter, and neuropsychological functioning.

METHODS

One hundred ninety-nine neurologically healthy adults received MRI and standardized neuropsychological assessment. MR images were spatially normalized and segmented by tissue type; relative white matter values in each of the four cerebral lobes in each hemisphere were computed. Subjects were divided into Younger (ages 21-30), Middle (ages 31-54), and Older (ages 55-79) age groups.

RESULTS

The Older group had significantly less overall relative white matter than the Middle group, who had significantly less overall relative white matter than the Younger participants (F (2, 193) = 5.42, p = 0.005). Differences in frontal lobe white matter were of largest magnitude, followed by temporal lobe (F (6, 579) = 3.32, p = 0.003). Age and frontal and temporal lobe white matter were primarily associated with performance on neuropsychological tests of executive functioning and memory. Mediational analysis suggested that frontal lobe white matter mediated the relationship between age and performance on tasks of executive functioning and memory.

CONCLUSIONS

The results confirm age-associated decline in frontal and temporal white matter, and age-related cognitive decline in several domains. Decline in neuropsychological functioning is, in part, mediated by a relative age-related reduction in frontal white matter.

Multisensory activation of the intraparietal area when classifying grating orientation: a functional magnetic resonance imaging study

Humans can judge grating orientation by touch. Previous studies indicate that the extrastriate cortex is involved in tactile orientation judgments, suggesting that this area is related to visual imagery. However, it has been unclear which neural mechanisms are crucial for the tactile processing of orientation, because visual imagery is not always required for tactile spatial tasks. We expect that such neural mechanisms involve multisensory areas, because our perception of space is highly integrated across modalities. The current study uses functional magnetic resonance imaging during the classification of grating orientations to evaluate the neural substrates responsible for the multisensory spatial processing of orientation. We hypothesized that a region within the intraparietal sulcus (IPS) would be engaged in orientation processing, regardless of the sensory modality. Sixteen human subjects classified the orientations of passively touched gratings and performed two control tasks with both the right and left hands. Tactile orientation classification activated regions around the right postcentral sulcus and IPS, regardless of the hand used, when contrasted with roughness classification of the same stimuli. Right-lateralized activation was confirmed in these regions by evaluating the hemispheric effects of tactile spatial processing with both hands. In contrast, visual orientation classification activated the left middle occipital gyrus when contrasted with color classification of the same stimuli. Furthermore, visual orientation classification activated a part of the right IPS that was also activated by the tactile orientation task. Thus, we suggest that a part of the right IPS is engaged in the multisensory spatial processing of grating orientation.

MDMA use is associated with increased spatial BOLD fMRI visual cortex activation in human MDMA users

Previous animal studies have demonstrated that 3,4-methylenedioxymethamphetamine (MDMA) exposure causes serotonin axotomy that is greatest in occipital cortex (including primary visual cortex) where serotonergic axons innervate neurons and blood vessels. Human MDMA users have altered serotonergic function and reduced gray matter density in occipital cortex. The fMRI BOLD method is potentially sensitive to both the neuronal and vascular consequences of MDMA-induced serotonin toxicity. To test the hypothesis that MDMA users have altered visual system function, we used the fMRI BOLD technique to assay visual cortical activation after photic stimulation in a group of adult MDMA users. Because MDMA users worldwide are polydrug users and therefore difficult to match to comparison groups in terms of polydrug exposure, we conducted a primary within-group analysis examining the correlation between lifetime episodes of MDMA exposure and measures of visual cortical activation. The within-group correlational analysis in the MDMA user group revealed that the degree of prior MDMA exposure was significantly positively correlated with the number of activated pixels for photic stimulation (r=0.582, p=0.007). A secondary between-group comparison of MDMA users with non-MDMA users found overall greater levels of polydrug exposure in the MDMA user cohort but no significant differences in visual cortical activation measures between the two groups. Additional research is needed to clarify the origin and significance of the current findings.

Age effects in time estimation: relationship to frontal brain morphometry

Compared with many other cognitive functions, relatively little is known about time representation in the brain. Recent work shows disrupted timing and time estimation in older adults, although it is unclear whether these effects are the result of normal aging or disease-related processes. The present study examined time estimation in persons across the adult lifespan who were free from significant medical or psychiatric history. Results showed older adults exhibited greater variability in time estimation, but no evidence for systematic acceleration or slowing emerged. This variability was correlated with performance on a variety of cognitive tests including attention, working memory and executive function. Although no relationship emerged between time estimation and EEG indices from central regions, multiple MRI indices were significantly correlated with time estimation. Stepwise regression showed volume of the supplementary motor area predicted variability in time estimation. These results indicate that healthy aging is associated with altered time estimation and suggest that changes in frontal brain regions mediate these effects.

Detecting white matter injury in sickle cell disease using voxel-based morphometry

OBJECTIVE

Sickle cell disease (SCD) is associated with cerebrovascular disease, cerebral infarction, and cognitive dysfunction. This study aimed to detect the presence and extent of white matter abnormalities in individuals with SCD using voxel-based morphometry (VBM).

METHODS

Thirty-six children and adolescents with SCD (age range, 9-24 years) and 31 controls (8-25 years) underwent magnetic resonance investigations using T1- and T2-weighted protocols. White and gray matter density maps were obtained from three-dimensional magnetic resonance imaging (MRI) data sets. Using VBM, we compared the maps between controls and SCD individuals with silent white matter infarct lesions (SCD+L; n = 16), and those without visible abnormality (SCD-L; n = 20).

RESULTS

In comparison with controls, intelligence quotients (IQs) were lower in both SCD groups irrespective of presence of visible lesions. VBM showed widespread bilateral white matter abnormalities in the SCD+L group, extending beyond the regions of focal infarction in the deep anterior and posterior white matter borderzones. Bilateral white matter abnormalities were also observed in the SCD-L group, in locations similar to those in the SCD+L group.

INTERPRETATION

VBM is sensitive to detection of widespread white matter injury in SCD patients in borderzones between arterial territories even in the absence of evidence of infarction. Those changes may contribute to cognitive deficits in this population.

Early life stress and morphometry of the adult anterior cingulate cortex and caudate nuclei

BACKGROUND

Early life stress (ELS) is linked to adult psychopathology and may contribute to long-term brain alterations, as suggested by studies of women who suffered childhood sexual abuse. We examine whether reported adverse ELS defined as stressful and/or traumatic adverse childhood events (ACEs) is associated with smaller limbic and basal ganglia volumes.

METHOD

265 healthy Australian men and women without psychopathology or brain disorders were studied. ACEs were assessed by the ELSQ and current emotional state by the DASS. Anterior cingulate cortex (ACC), hippocampus, amygdala, and caudate nucleus volumes were measured from T1-weighted MRI. Analyses examined ROI volumetric associations with reported ACEs and DASS scores.

RESULTS

Participants with greater than two ACEs had smaller ACC and caudate nuclei than those without ACEs. A significant association between total ACEs and ROI volumes for these structures was observed. Regression analysis also revealed that ELS was more strongly associated than current emotional state (DASS) with these ROI volumes.

CONCLUSIONS

Reported ELS is associated with smaller ACC and caudate volumes, but not the hippocampal or amygdala volumes. The reasons for these brain effects are not entirely clear, but may reflect the influence of early stress and traumatic events on the developing brain.

Neural underpinning of postural responses to visual field motion

Numerous results emerging from current research strongly implicate the effect of Visual Field Motion on the organization of postural responses. However, this is the first empirical study exploring the neural substrates underlying the subjects' response to Visual Field Motion. Two separate experiments were conducted to investigate the subject responses to Visual Field Motion. In the first experiment, the standing subjects were exposed to Visual Field Motion in the VR environment. In the second experiment, the recumbent subjects viewed the same Visual Field Motion while in a MRI scanner. A virtual reality (VR) prototype of the moving room paradigm [Lee, D.N., Aronson, E., 1974. Visual proprioceptive control of standing in human infants. Perception & Psychophysics 15, 529-532] was developed to simulate various optic flow patterns in a controlled VR environment. Postural responses (center of pressure, body kinematics, vection, egomotion) and brain activation patterns (fMRI signals) were examined. The subjects experienced egomotion and have reported vection in both experiments only when certain attributes of Visual Field Motion were introduced. This was accompanied by significant activation of specific brain structures, including prefrontal, parietal cortices and bilateral cerebellum. We propose the existence of functional interactions between modality specific areas of the brain involved in postural responses to Visual Field Motion (VFM).

Age-related changes in brain activation during a delayed item recognition task

To test competing models of age-related changes in brain functioning (capacity limitation, neural efficiency, compensatory reorganization, and dedifferentiation), young (n=40; mean age=25.1 years) and elderly (n=18; mean age=74.4 years) subjects performed a delayed item recognition task for visually presented letters with three set sizes (1, 3, or 6 letters) while being scanned with BOLD fMRI. Spatial patterns of brain activity corresponding to either the slope or y-intercept of fMRI signal with respect to set size during memory set encoding, retention delay, or probe stimulus presentation trial phases were compared between elder and young populations. Age effects on fMRI slope during encoding and on fMRI y-intercept during retention delay were consistent with neural inefficiency; age effects on fMRI slope during retention delay were consistent with dedifferentiation. None of the other fMRI signal components showed any detectable age effects. These results suggest that, even within the same task, the nature of brain activation changes with aging can vary based on cognitive process engaged.

Cerebral changes during performance of overlearned arbitrary visuomotor associations

The posterior parietal cortex (PPC) is known to be involved in the control of automatic movements that are spatially guided, such as grasping an apple. We considered whether the PPC might also contribute to the performance of visuomotor associations in which stimuli and responses are linked arbitrarily, such as producing a certain sound for a typographical character when reading aloud or pressing pedals according to the color of a traffic light when driving a motor vehicle. The PPC does not appear to be necessary for learning new arbitrary visuomotor associations, but with extensive training, the PPC can encode nonspatial sensory features of task-relevant cues. Accordingly, we have tested whether the contributions of the PPC might become apparent once arbitrary sensorimotor mappings are overlearned. We have used functional magnetic resonance imaging to measure cerebral activity while subjects were learning novel arbitrary visuomotor associations, overlearning known mappings, or attempting to learn frequently changing novel mappings. To capture the dynamic features of cerebral activity related to the learning process, we have compared time-varying modulations of activity between conditions rather than average (steady-state) responses. Frontal, striatal, and intraparietal regions showed decreasing or stable activity when subjects learned or attempted to learn novel associations, respectively. Importantly, the same frontal, striatal, and intraparietal regions showed time-dependent increases in activity over time as the mappings become overlearned, i.e., despite time-invariant behavioral responses. The automaticity of these mappings predicted the degree of intraparietal changes, indicating that the contribution of the PPC might be related to a particular stage of the overlearning process. We suggest that, as the visuomotor mappings become robust to interference, the PPC may convey relevant sensory information toward the motor cortex. More generally, our findings illustrate how rich cerebral dynamics can underlie stable behavior.

Functionally segregated neural substrates for arbitrary audiovisual paired-association learning

To clarify the neural substrates and their dynamics during crossmodal association learning, we conducted functional magnetic resonance imaging (MRI) during audiovisual paired-association learning of delayed matching-to-sample tasks. Thirty subjects were involved in the study; 15 performed an audiovisual paired-association learning task, and the remainder completed a control visuo-visual task. Each trial consisted of the successive presentation of a pair of stimuli. Subjects were asked to identify predefined audiovisual or visuo-visual pairs by trial and error. Feedback for each trial was given regardless of whether the response was correct or incorrect. During the delay period, several areas showed an increase in the MRI signal as learning proceeded: crossmodal activity increased in unimodal areas corresponding to visual or auditory areas, and polymodal responses increased in the occipitotemporal junction and parahippocampal gyrus. This pattern was not observed in the visuo-visual intramodal paired-association learning task, suggesting that crossmodal associations might be formed by binding unimodal sensory areas via polymodal regions. In both the audiovisual and visuo-visual tasks, the MRI signal in the superior temporal sulcus (STS) in response to the second stimulus and feedback peaked during the early phase of learning and then decreased, indicating that the STS might be key to the creation of paired associations, regardless of stimulus type. In contrast to the activity changes in the regions discussed above, there was constant activity in the frontoparietal circuit during the delay period in both tasks, implying that the neural substrates for the formation and storage of paired associates are distinct from working memory circuits.