Frequency dependence and gender effects in visual cortical regions involved in temporal frequency dependent pattern processing

Distinct patterns of spatial attentional modulation of steady-state visual evoked magnetic fields (SSVEFs) in subdivisions of the human early visual cortex

In recent years, steady-state visual evoked potentials (SSVEPs) became an increasingly valuable tool to investigate neural dynamics of competitive attentional interactions and brain-computer interfaces. This is due to their good signal-to-noise ratio, allowing for single-trial analysis, and their ongoing oscillating nature that enables to analyze temporal dynamics of facilitation and suppression. Given the popularity of SSVEPs, it is surprising that only a few studies looked at the cortical sources of these responses. This is in particular the case when searching for studies that assessed the cortical sources of attentional SSVEP amplitude modulations. To address this issue, we used a typical spatial attention task and recorded neuromagnetic fields (MEG) while presenting frequency-tagged stimuli in the left and right visual fields, respectively. Importantly, we controlled for attentional deployment in a baseline period before the shifting cue. Subjects either attended to a central fixation cross or to two peripheral stimuli simultaneously. Results clearly showed that signal sources and attention effects were restricted to the early visual cortex: V1, V2, hMT+, precuneus, occipital-parietal, and inferior-temporal cortex. When subjects attended to central fixation first, shifting attention to one of the peripheral stimuli resulted in a significant activation increase for the to-be-attended stimulus with no activation decrease for the to-be-ignored stimulus in hMT+ and inferio-temporal cortex, but significant SSVEF decreases from V1 to occipito-parietal cortex. When attention was first deployed to both rings, shifting attention away from one ring basically resulted in a significant activation decrease in all areas for the then-to-be-ignored stimulus.

Generation of a whole-brain hemodynamic response function and sex-specific differences in cerebral processing of mechano-sensation in mice detected by BOLD fMRI

BOLD fMRI has become a prevalent method to study cerebral sensory processing in rodent disease models, including pain and mechanical hypersensitivity. fMRI data analysis is frequently combined with a general-linear-model (GLM) -based analysis, which uses the convolution of a hemodynamic response function (HRF) with the stimulus paradigm. However, several studies indicated that the HRF differs across species, sexes, brain structures, and experimental factors, including stimulation modalities or anesthesia, and hence might strongly affect the outcome of BOLD analyzes. While considerable work has been done in humans and rats to understand the HRF, much less is known in mice. As a prerequisite to investigate mechano-sensory processing and BOLD fMRI data in male and female mice, we (1) designed a rotating stimulator that allows application of two different mechanical modalities, including innocuous von Frey and noxious pinprick stimuli and (2) determined and statistically compared HRFs across 30 brain structures and experimental conditions, including sex and, stimulus modalities. We found that mechanical stimulation lead to brain-wide BOLD signal changes thereby allowing extraction of HRFs from multiple brain structures. However, we did not find differences in HRFs across all brain structures and experimental conditions. Hence, we computed a whole-brain mouse HRF, which is based on 88 functional scans from 30 mice. A comparison of this mouse-specific HRF with our previously reported rat-derived HRF showed significantly slower kinetics in mice. Finally, we detected pronounced differences in cerebral BOLD activation between male and female mice with mechanical stimulation, thereby exposing divergent processing of noxious and innocuous stimuli in both sexes.

Variation within the visually evoked neurovascular coupling response of the posterior cerebral artery is not influenced by age or sex

Neurovascular coupling (NVC) is the temporal and spatial coordination between local neuronal activity and regional cerebral blood flow. The literature is unsettled on whether age and/or sex affect NVC, which may relate to differences in methodology and the quantification of NVC in small sample-sized studies. The aim of this study was to 1) determine the relative and combined contribution of age and sex to the variation observed across several distinct NVC metrics (n = 125, 21–66 yr; 41 males) and 2) present an approach for the comprehensive systematic assessment of the NVC response using transcranial Doppler ultrasound. NVC was measured as the relative change from baseline (absolute and percent change) assessing peak, mean, and total area under the curve (tAUC) of cerebral blood velocity through the posterior cerebral artery (PCAv) during intermittent photic stimulation. In addition, the NVC waveform was compartmentalized into distinct regions, acute (0–9 s), mid (10–19 s), and late (20–30 s), following the onset of photic stimulation. Hierarchical multiple regression modeling was used to determine the extent of variation within each NVC metric attributable to demographic differences in age and sex. After controlling for differences in baseline PCAv, the R² data suggest that 1.6%, 6.1%, 1.1%, 3.4%, 2.5%, and 4.2% of the variance observed within mean, peak, tAUC, acute, mid, and late response magnitude is attributable to the combination of age and sex. Our study reveals that variability in NVC response magnitude is independent of age and sex in healthy human participants, aged 21–66 yr.

NEW & NOTEWORTHY We assessed the variability within the neurovascular coupling response attributable to age and sex (n = 125, 21–66 yr; 41 male). Based on the assessment of posterior cerebral artery responses to visual stimulation, 0%–6% of the variance observed within several metrics of NVC response magnitude are attributable to the combination of age and sex. Therefore, observed differences between age groups and/or sexes are likely a result of other physiological factors.

Gender differential item functioning analysis in measuring computational thinking disposition among secondary school students

Computational thinking refers to the cognitive processes underpinning the application of computer science concepts and methodologies to the methodical approach and creation of a solution to a problem. The study aims to determine how students' cognitive, affective, and conative dispositions in using computational thinking are influenced by a gender. This study used a survey research design with quantitative approach. Five hundred thirty-five secondary school students were sampled using probability sampling with the Computational Thinking Disposition Instrument (CTDI). WINSTEPS version 3.71.0 software was subsequently employed to assess the Gender Differential item functioning (GDIF) including reliability and validity with descriptive statistics were employed to assess students' disposition toward practicing computational thinking. In addition to providing implications for the theory, the data give verifiable research that the CT disposition profile consists of three constructs. In addition, the demonstrated CTDI has good GDIF features, which may be employed to evaluate the efficacy of the application of CT in the Malaysian curriculum by measuring the level of CT in terms of the disposition profile of students.

Hemodynamic responses are abnormal in isolated cervical dystonia

Neuroimaging studies using functional magnetic resonance imaging (fMRI), which measures brain activity by detecting the changes in blood oxygenation levels, are advancing our understanding of the pathophysiology of dystonia. Neurobiological disturbances in dystonia, however, may affect neurovascular coupling and impact the interpretability of fMRI studies. We evaluated here whether the hemodynamic response patterns during a behaviorally matched motor task are altered in isolated cervical dystonia (CD). Twenty-five CD patients and 25 healthy controls (HCs) underwent fMRI scanning during a paced finger tapping task (nondystonic task in patients). Imaging data were analyzed using a constrained principal component analysis-a statistical method that combines regression analysis and principal component analysis and enables the extraction of task-related functional networks and determination of the spatial and temporal hemodynamic response patterns associated with the task performance. Data from three patients and two controls were removed due to excessive movement. No significant differences in demographics or motor performance were observed. Three task-associated functional brain networks were identified. During task performance, reduced hemodynamic responses were seen in a sensorimotor network and in a network that included key nodes of the default mode, executive control and visual networks. During rest, reductions in hemodynamic responses were seen in the cognitive/visual network. Lower hemodynamic responses within the primary sensorimotor network in patients were correlated with the increased dystonia severity. Pathophysiological disturbances in isolated CD, such as alterations in inhibitory signaling and dopaminergic neurotransmission, may impact neurovascular coupling. Not accounting for hemodynamic response differences in fMRI studies of dystonia could lead to inaccurate results and interpretations.

A cortical rat hemodynamic response function for improved detection of BOLD activation under common experimental conditions

For a reliable estimation of neuronal activation based on BOLD fMRI measurements an accurate model of the hemodynamic response is essential. Since a large part of basic neuroscience research is based on small animal data, it is necessary to characterize a hemodynamic response function (HRF) which is optimized for small animals. Therefore, we have determined and investigated the HRFs of rats obtained under a variety of experimental conditions in the primary somatosensory cortex. Measurements were performed on animals of different sex and strain, under different anesthetics, with and without ventilation and using different stimulation modalities. All modalities of stimulation used in this study induced neuronal activity in the primary somatosensory cortex or in subcortical regions. Since the HRFs of the BOLD responses in the primary somatosensory cortex showed a close concordance for the different conditions, we were able to determine a cortical rat HRF. This HRF is based on 143 BOLD measurements of 76 rats and can be used for statistical parametric mapping. It showed substantially faster progression than the human HRF, with a maximum after 2.8 ± 0.8 s, and a following undershoot after 6.1 ± 3.7 s. If the rat HRF was used statistical analysis of rat data showed a significantly improved detection performance in the somatosensory cortex in comparison to the commonly used HRF based on measurements in humans.

Influence of contrast-reversing frequency on the amplitude and spatial distribution of visual cortex hemodynamic responses

Visual stimulation is one of the most commonly used paradigms for cerebral cortex function investigation. Experiments typically involve presenting to a volunteer a black-and-white checkerboard with contrast-reversing at a frequency of 4 to 16 Hz. The aim of the present study was to investigate the influence of the flickering frequency on the amplitude of changes in the concentration of oxygenated and deoxygenated hemoglobin. The hemoglobin concentrations were assessed with the use of a high resolution diffuse optical tomography method. Spatial distributions of changes in hemoglobin concentrations overlaying the visual cortex are shown for various stimuli frequencies. Moreover, the hemoglobin concentration changes obtained for different source-detector separations (from 1.5 to 5.4 cm) are presented. Our results demonstrate that the flickering frequency had a statistically significant effect on the induced oxyhemoglobin changes (p < 0,001). The amplitude of oxy hemoglobin concentration changes at a frequency of 8 Hz was higher in comparison with that measured at 4 Hz :[median(25th-75thpercentiles) 1.24 (0.94-1.71) vs. 0.92(0.73-1.28)µM, p < 0.001]; 12 Hz:[1.24 (0.94-1.71) vs. 1.04 (0.78-1.32) µM, p < 0.001]; and 16 Hz:[1.24 (0.94-1.71) vs. 1.15(0.87-1.48) µM, p < 0.001]. No significant differences were observed between the size of an area of activation for various frequencies. The demonstrated superiority of 8 Hz over other frequencies can advance understanding of visual stimulations and help guide future fNIRS protocols.

Cerebrovascular Hemodynamics in Women

Sex and gender, as biological and social factors, significantly influence health outcomes. Among the biological factors, sex differences in vascular physiology may be one specific mechanism contributing to the observed differences in clinical presentation, response to treatment, and clinical outcomes in several vascular disorders. This review focuses on the cerebrovascular bed and summarizes the existing literature on sex differences in cerebrovascular hemodynamics to highlight the knowledge deficit that exists in this domain. The available evidence is used to generate mechanistically plausible and testable hypotheses to underscore the unmet need in understanding sex-specific mechanisms as targets for more effective therapeutic and preventive strategies.

New insights into the role of motion and form vision in neurodevelopmental disorders

A selective deficit in processing the global (overall) motion, but not form, of spatially extensive objects in the visual scene is frequently associated with several neurodevelopmental disorders, including preterm birth. Existing theories that proposed to explain the origin of this visual impairment are, however, challenged by recent research. In this review, we explore alternative hypotheses for why deficits in the processing of global motion, relative to global form, might arise. We describe recent evidence that has utilised novel tasks of global motion and global form to elucidate the underlying nature of the visual deficit reported in different neurodevelopmental disorders. We also examine the role of IQ and how the sex of an individual can influence performance on these tasks, as these are factors that are associated with performance on global motion tasks, but have not been systematically controlled for in previous studies exploring visual processing in clinical populations. Finally, we suggest that a new theoretical framework is needed for visual processing in neurodevelopmental disorders and present recommendations for future research.

BOLD signal change and contrast reversing frequency: an event-related fMRI study in human primary visual cortex

It is believed that human primary visual cortex (V1) increases activity with increasing temporal frequency of a visual stimulus. Two kinds of visual stimulus were used in the previous studies, one is patterned-flash stimulus with a fixed onset period and an increasing average luminance with the increase of temporal frequency, the other is contrast reversing flickering checkerboard or grating with a constant average luminance across different temporal frequencies. That hemodynamic responses change as a function of reversal frequency of contrast reversing checkerboard is at odds with neurophysiological studies in animals and neuroimaging studies in humans. In the present study, we addressed the relationship between reversal frequency of contrast reversing checkerboard and hemodynamic response in human V1 using an event-related experimental paradigm and found that the transient characteristics of blood oxygenation level dependent response in human V1 depended very little on the reversal frequency of a contrast reversing checkerboard.

Gender characteristics of cerebral hemodynamics during complex cognitive functioning

Functional Transcranial Doppler sonography (fTCD) has been applied to assess peak mean cerebral blood flow velocity (MFV) with a high temporal resolution during cognitive activation. Yet, little attention has been devoted to gender-related alterations of MFV, including spectral analysis. In healthy subjects, fTCD was used to investigate a series of cerebral hemodynamic parameters in the middle cerebral arteries (MCA) during the Trail Making Tests (TMT), a means of selective attention and complex cognitive functioning. In females, there was a frequency peak at 0.375 Hz in both MCA, and we observed a dynamic shift in hemispheric dominance during that condition. Further, after the start phase, there was an MFV decline during complex functioning for the entire sample. These novel results suggest condition-specific features of cerebral hemodynamics in females, and it adds to the notion that gender is a fundamental confounder of brain physiology.

Gender differences in the functional and structural neuroanatomy of mathematical cognition

Despite ongoing debate about the nature of gender differences in mathematics achievement, little is known about gender similarities and differences in mathematical cognition at the neural level. We used fMRI to compare brain responses in 25 females and 24 males during a mental arithmetic task involving 3-operand addition and subtraction. We also used voxel-based morphometry (VBM) to examine gender differences in brain structure. Although females and males did not differ in accuracy or response times (effect size d<0.3), significant gender differences in functional brain activation were observed in the right dorsal and ventral visuospatial information processing streams (d>1.1). Males showed greater dorsal stream activation in the right intra-parietal sulcus areas important for numerical cognition, and angular gyrus regions of the default mode network that are typically deactivated during complex cognitive tasks, as well as greater ventral stream activation in the right lingual and parahippocampal gyri. VBM revealed an opposite pattern of gender differences-compared to males, females had greater regional density and greater regional volume in dorsal and ventral stream regions where males showed greater fMRI activation. There were no brain areas where females showed greater functional activation than males, and no brain areas where males showed greater structural density or volume than females. Our findings provide evidence for gender differences in the functional and structural organization of the right hemisphere brain areas involved in mathematical cognition. Together with the lack of behavioral differences, our results point to more efficient use of neural processing resources in females.

Hemispheric asymmetries for temporal information processing: Transient detection versus sustained monitoring

This study investigated functional differences in the processing of visual temporal information between the left and right hemispheres (LH and RH). Participants indicated whether or not a checkerboard pattern contained a temporal gap lasting between 10 and 40 ms. When the stimulus contained a temporal signal (i.e. a gap), responses were more accurate for the right visual field-left hemisphere (RVF-LH) than for the left visual field-right hemisphere (LVF-RH). This RVF-LH advantage was larger for the shorter gap durations (Experiments 1 and 2), suggesting that the LH has finer temporal resolution than the RH, and is efficient for transient detection. In contrast, for noise trials (i.e. trial without temporal signals), there was a LVF-RH advantage. This LVF-RH advantage was observed when the entire stimulus duration was long (240 ms, Experiment 1), but was eliminated when the duration was short (120 ms, Experiment 2). In Experiment 3, where the gap was placed toward the end of the stimulus presentation, a LVF-RH advantage was found for noise trials whereas the RVF-LH advantage was eliminated for signal trials. It is likely that participants needed to monitor the stimulus for a longer period of time when the gap was absent (i.e. noise trials) or was placed toward the end of the presentation. The RH may therefore be more efficient in the sustained monitoring of visual temporal information whereas the LH is more efficient for transient detection.

Gender-specific left-right asymmetries in human visual cortex

The structural correlates of gender differences in visuospatial processing are essentially unknown. Our quantitative analysis of the cytoarchitecture of the human primary visual cortex [V1/Brodmann area 17 (BA17)], neighboring area V2 (BA18), and the cytoarchitectonic correlate of the motion-sensitive complex (V5/MT+/hOc5) shows that the visual areas are sexually dimorphic and that the type of dimorphism differs among the areas. Gender differences exist in the interhemispheric asymmetry of hOc5 volumes and in the right-hemispheric volumetric ratio of hOc5 to BA17, an area that projects to V5/MT+/hOc5. Asymmetry was also observed in the surface area of hOc5 but not in its cortical thickness. The differences give males potentially more space in which to process additional information, a finding consistent with superior male processing in particular visuospatial tasks, such as mental rotation. Gender differences in hOc5 exist with similar volume fractions of cell bodies, implying that, overall, the visual neural circuitry is similar in males and females.

A spatial and temporal comparison of hemodynamic signals measured using optical and functional magnetic resonance imaging during activation in the human primary visual cortex

Functional near infrared spectro-imaging (fNIRSI) is potentially a very useful technique for obtaining information about the underlying physiology of the blood oxygenation level dependent (BOLD) signal used in functional magnetic resonance imaging (fMRI). In this paper the temporal and spatial statistical characteristics of fNIRSI data are compared to those of simultaneously acquired fMRI data in the human visual cortex during a variable-frequency reversing checkerboard activation paradigm. Changes in the size of activated volume caused by changes in checkerboard reversal frequency allowed a comparison of the behavior of the spatial responses measured by the two imaging methods. fNIRSI and fMRI data were each analyzed using standard correlation and fixed-effect group analyses of variance pathways. The statistical significance of fNIRSI data was found to be much lower than that of the fMRI data, due mainly to the low signal-to-noise of the measurements. Reconstructed images also showed that, while the time-course of changes in the oxy-, deoxy-, and total hemoglobin concentrations all exhibit high correlation with that of the BOLD response, the changes in the volume of tissue measured as "activated" by the BOLD response demonstrate a closer similarity to the corresponding changes in the oxy- and total hemoglobin concentrations than to that of the deoxyhemoglobin.

A spatial and temporal comparison of hemodynamic signals measured using optical and functional magnetic resonance imaging during activation in the human primary visual cortex

Functional near infrared spectro-imaging (fNIRSI) is potentially a very useful technique for obtaining information about the underlying physiology of the blood oxygenation level dependent (BOLD) signal used in functional magnetic resonance imaging (fMRI). In this paper the temporal and spatial statistical characteristics of fNIRSI data are compared to those of simultaneously acquired fMRI data in the human visual cortex during a variable-frequency reversing checkerboard activation paradigm. Changes in the size of activated volume caused by changes in checkerboard reversal frequency allowed a comparison of the behavior of the spatial responses measured by the two imaging methods. fNIRSI and fMRI data were each analyzed using standard correlation and fixed-effect group analyses of variance pathways. The statistical significance of fNIRSI data was found to be much lower than that of the fMRI data, due mainly to the low signal-to-noise of the measurements. Reconstructed images also showed that, while the time-course of changes in the oxy-, deoxy-, and total hemoglobin concentrations all exhibit high correlation with that of the BOLD response, the changes in the volume of tissue measured as "activated" by the BOLD response demonstrate a closer similarity to the corresponding changes in the oxy- and total hemoglobin concentrations than to that of the deoxyhemoglobin.

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.

Group Analysis of FMRI and NIR Data Simultaneously Acquired During Visual Stimulation in Humans

We use our new combined functional near infrared spectro-imaging (fNIRSI) and magnetic resonance imaging (MRJ) technique to compare fMRI and fNIRSI data at different activation conditions, to obtain new information about the underlying physiology of the blood oxygen level dependent (BOLD) signal used in fMRI, and to assess statistical characteristics of spatial functional information provided by the group analysis of fNIRSI data. To achieve these goals we have acquired simultaneously fNIRSI and fMRI data during the presentation of the checkerboard reversing with different frequencies, and analyzed these data following the standard correlation and group analysis of variance pathway used in functional neuroimaging. . We have found that while the time courses of oxy-, deoxy-, and total- hemoglobin responses are equally well correlated with the time course of the BOLD response, the spatial pattern and magnitude of the BOLD response is better related to those of the oxy-, and total- hemoglobin responses rather than to the deoxyhemoglobin response. The statistical significance of the fNIRSI group maps is inferior to that of fMRI, and can be particularly compromised by the anatomical features of subjects.

Neuroplasticity as a Double-edged Sword: Deaf Enhancements and Dyslexic Deficits in Motion Processing

We examined the hypothesis that aspects of processing that are most modifiable by experience (i.e., “plastic”) display the most vulnerability in developmental disorders and the most compensatory enhancement after sensory deprivation. A large literature reports that motion processing and magnocellular visual function is selectively deficient in dyslexia. A smaller literature reports enhancements in such functions in deaf individuals. However, studies with dyslexic and deaf individuals have used different experimental paradigms to assess visual function, and no research has yet examined both sides of modifiability (i.e., enhancements and deficits) using the same experimental paradigm. In the present research, visual function was compared in dyslexic (n = 15), deaf (n = 17), and control adults by using automated peripheral kinetic and foveal static perimetry. In the kinetic perimetry task, the dyslexic group showed deficits ( p &lt; .003), whereas the deaf group showed enhancements ( p &lt; .001) for detecting moving light points in the periphery. In the foveal static perimetry task, neither the dyslexic ( p = .866) nor the deaf ( p = .632) group differed significantly from controls in foveal contrast sensitivity thresholds, and no group or individual approached ceiling performance on this task. Taken together, the present data bridge previous literatures and suggest that motion processing tasks are selectively modifiable, either to decrement or enhancement, whereas foveal contrast sensitivity does not differ in dyslexic or deaf groups.

Sex differences in the cerebral BOLD signal response to painful heat stimuli

There are limited data addressing the question of sex differences in pain-related cerebral processing. This study examined whether pain-related blood oxygenation level-dependent (BOLD) signal change measured with functional magnetic resonance imaging (fMRI) demonstrated sex differences, under conditions of equivalent pain perception. Twenty-eight healthy volunteers (17 women, 11 men) were subject to a fMRI scan while noxious heat stimuli were applied to the dorsum of the left foot. Significant BOLD signal modulation was observed in several nociceptive processing regions of interest (ROIs) in all subjects. There were no sex differences in the spatial extent of BOLD signal change for any ROI, but the signal amplitude was lower for women in most ROIs and significantly so for the primary somatosensory cortex (S1), the midanterior cingulate cortex, and the dorsolateral prefrontal cortex (DLPFC). The BOLD signal response could be positive or negative, and frequently, both polarities were observed within a single ROI. In most ROIs, women show proportionately more voxels with negative signal change than men, and this difference was statistically significant for the S1 and the DLPFC. The time course of the negative signal change was very similar to that of the positive signal change, suggesting that the latter was not "driving" the former. The location of negative and positive clusters formed distinct patterns in several of the ROIs, and these patterns suggest something other than a local "steal" phenomenon as an explanation for the negative signal changes. Sex differences in baseline cerebral blood flow may contribute to the BOLD signal differences observed in this study.

Does egocentric mental rotation elicit sex differences?

Mental rotation tests traditionally show a male performance advantage. Some neuroimaging studies have reported sex-specific cortical activation patterns during mental rotation. However, these experiments used abstract stimuli and some studies did not systematically exclude performance as a confounding variable. The mental rotation of hands and hand-related objects, compared to abstract objects, is known to evoke an egocentric motor strategy. In this study, we used fMRI to explore potential gender-specific cortical activation patterns for the mental rotation of hands and tools in a sample with an adequate and equal performance for men and women. We found a common neural substrate for men and women comprising superior parietal lobe, dorsolateral premotor cortex, and extrastriate occipital areas, compatible with an egocentric motor strategy for the mental rotation of hands and tools. Sex differences were modest and limited to the mental rotation of hands. Women recruited more left ventral premotor cortex, which could imply that women rely more on imitation or use more perceptual comparisons. Men, on the other hand, drafted more the lingual gyrus, possibly referring to more extensive semantic or early visual processing. We conclude that men and women use a very similar motor strategy during egocentric mental rotation with a potential gender-specific accent.

Activation in the MT-complex during visual perception of apparent motion and temporal succession

Previous studies have shown that MT (i.e., the MT-complex) is activated during visual perception of apparent motion. To further explore the function of MT, we measured activation in MT by positron emission tomography (PET) using a broad range of stroboscopic stimulus events in which (a) the frame rate was so fast that observers perceived stimulus frames as simultaneous, (b) the frame rate was slower and generated compelling impressions of apparent motion, or (c) the frame rate was so slow that observers perceived temporal succession (successive views of the same objects at different locations) instead of motion. As expected, the simultaneity condition showed no activation (reliable increase in regional cerebral blood flow, rCBF) in MT whereas the motion condition showed activation in both left and right MT. However, the succession condition showed even stronger activation in left and right MT than did the motion condition. MT seems implicated in perception of retinal stimuli as successive views of the same object at different locations whether or not the views are connected by apparent motion.

Correlation between the amplitude of cortical activation and reaction time: a functional MRI study

OBJECTIVE

We sought to examine the correlation between reaction time and the amplitude of cortical activation during the performance of a visuomotor response-time task in a functional MRI (fMRI) experiment. We hypothesized that the fMRI blood oxygenation level-dependent (BOLD) amplitude may have a negative correlation with a subject's reaction time: the lower the amplitude within the cortical areas along the visuomotor pathway, the slower the response. A larger amplitude of the fMRI signal would reflect faster response times.

SUBJECTS AND METHODS

During a single-event fMRI experiment, the reaction times (in milliseconds) of 32 right-handed subjects responding to a visual cue were recorded. Analysis of the single-event paradigm using Statistical Parametric Mapping (SPM99) was performed, activation maps were produced for each subject, and then a random effects group analysis was performed. The maximum amplitudes of cortical activation (percent signal change) in four activated cortical regions were estimated and tabulated. The regions of interest included were the right and left occipital visual cortices, the supplementary motor area, and the left sensorimotor area. Simple and multiple regressions were performed between the mean reaction times of the subjects and the BOLD amplitudes in each region of interest and for the composite region of interest.

RESULTS

The results showed significant negative associations between the reaction times and maximum amplitudes in the right occipital, left occipital, and left sensorimotor area cortical regions (p < 0.05). However, no significant association was found between reaction times and the amplitude within the supplementary motor area. When the effects of age and sex on these associations were analyzed, we found that age had an impact on the results for individual regions of interest in the left occipital and left sensorimotor areas, but the composite amplitude of activation remained significantly correlated with reaction times.

CONCLUSION

The degree of signal change in BOLD fMRI response of the right occipital, left occipital, and left sensorimotor areas reflects the speed of performance during the visuomotor response time task by the subject. Thus, the amplitude of activation can be used as one parameter to assess change in function.

The temporal frequency tuning of human visual cortex investigated using synthetic aperture magnetometry

Using synthetic aperture magnetometry (SAM) analyses of magnetoencephalographic (MEG) data, we investigated the variation in cortical response magnitude and frequency as a function of stimulus temporal frequency. In two separate experiments, a reversing checkerboard stimulus was used in the right or left lower visual field at frequencies from 0 to 21 Hz. Average temporal frequency tuning curves were constructed for regions-of-interest located within medial visual cortex and V5/MT. In medial visual cortex, it was found that both the frequency and magnitude of the steady-state response varied as a function of the stimulus frequency, with multiple harmonics of the stimulus frequency being found in the response. The maximum fundamental response was found at a stimulus frequency of 8 Hz, whilst the maximum broadband response occurred at 4 Hz. In contrast, the magnitude and frequency content of the evoked onset response showed no dependency on stimulus frequency. Whilst medial visual cortex showed a power increase during stimulation, extra-striate areas such as V5/MT exhibited a bilateral event-related desynchronisation (ERD). The frequency content of this ERD did not depend on the stimulus frequency but was a broadband power reduction across the 5-20 Hz frequency range. The magnitude of this ERD within V5/MT was strongly low-pass tuned for stimulus frequency, and showed only a moderate preference for stimuli in the contralateral visual field.

Gender-specific Differences of Hypometabolism in mTLE: Implication for Cognitive Impairments

PURPOSE

To determine gender differences of hypometabolism and their implications for cognitive impairment in patients with medically refractory mesial temporal lobe epilepsy (mTLE).

METHODS

Regional cerebral glucose metabolism (rCMRGlu) was studied in 42 patients (21 male, 21 female) with either left- or right-sided mTLE (22 left, 20 right) and in 12 gender- and age-matched healthy controls during resting wakefulness and in 12 sex- and age-matched healthy controls. Clinical characteristics were balanced across the patient subgroups. All patients were subjected to neuropsychological assessment: 41 patients had histologic changes of definite or probable hippocampal sclerosis.

RESULTS

Data analysis based on pixel-by-pixel comparisons and on a laterality index of regions of interest (ROIs) showed significant depressions of the mean rCMRGlu extending beyond the mesiotemporal region and temporolateral cortex to extratemporal regions including the frontoorbital and insular cortex in mTLE patients. Extramesiotemporal hypometabolism prevailed in the male patients. Metabolic asymmetry in temporal and frontal regions was related to performance in the Trail-Making Test and WAIS-R subitems.

CONCLUSIONS

Our data showed a gender-specific predominance of extramesiotemporal hypometabolism in male patients with mTLE related to abnormalities of temporal and frontal lobe functions.

Refractive anomalies and visual activation in functional magnetic resonance imaging (fMRI): a versatile and low-cost MR-compatible device to correct a potential confound

PURPOSE

To develop a magnetic resonance (MR)-compatible, versatile, easy-to-use, and low-cost device for refractive correction.

MATERIALS AND METHODS

We retrospectively evaluated the application and practicability of the refractive correction in 110 subjects who had participated in various functional MR imaging (fMRI) studies with complex visual stimulation paradigms since the introduction of the MR-compatible lens frame at our site. The subjects consisted of 31 patients with Parkinson's disease (age range, 40-85; mean age, 63.2 years) and 79 healthy volunteers (age range, 18-79; mean age, 46.7 years).

RESULTS

In volunteers, experimentally induced myopia caused a substantial (>20%) reduction of the blood oxygenation level dependent (BOLD) response to a flickering dartboard.

CONCLUSION

Refractive errors (and the resulting optical blur) may play a nonnegligible role as a possible interfering factor in fMRI experiments with visual stimuli. The MR-compatible frame (fitted with appropriate lenses) used in this study affords full refractive correction at reasonable cost and preparation time.