The neural substrate of gesture recognition

Previous studies have linked action recognition with a particular pool of neurons located in the ventral premotor cortex, the posterior parietal cortex and the superior temporal sulcus (the mirror neuron system). However, it is still unclear if transitive and intransitive gestures share the same neural substrates during action-recognition processes. In the present study, we used event-related functional magnetic resonance imaging (fMRI) to assess the cortical areas active during recognition of pantomimed transitive actions, intransitive gestures, and meaningless control actions. Perception of all types of gestures engaged the right pre-supplementary motor area (pre-SMA), and bilaterally in the posterior superior temporal cortex, the posterior parietal cortex, occipitotemporal regions and visual cortices. Activation of the posterior superior temporal sulcus/superior temporal gyrus region was found in both hemispheres during recognition of transitive and intransitive gestures, and in the right hemisphere during the control condition; the middle temporal gyrus showed activation in the left hemisphere when subjects recognized transitive and intransitive gestures; activation of the left inferior parietal lobe and intraparietal sulcus (IPS) was mainly observed in the left hemisphere during recognition of the three conditions. The most striking finding was the greater activation of the left inferior frontal gyrus (IFG) during recognition of intransitive actions. Results show that a similar neural substrate, albeit, with a distinct engagement underlies the cognitive processing of transitive and intransitive gestures recognition. These findings suggest that selective disruptions in these circuits may lead to distinct clinical deficits.     

Recovery of semantic word processing in transcortical sensory aphasia: a functional magnetic resonance imaging study

In a previous functional magnetic resonance imaging (fMRI) study with normal subjects, we demonstrated regions related to conceptual-semantic word processing around the first frontal sulcus (BA 9) and the posterior parietal lobe (BA 7/40) in agreement with several previous reports. We had the possibility, using the same fMRI paradigm, to study two consecutive cases with left middle cerebral artery (MCA) infarction (RC and HP) and lesions affecting either solely the pre-frontal (HP) or both the pre-frontal and posterior parietal part of the network activated in normal subjects (RC). Both patients showed transcortical sensory aphasia (TSA) on acute assessment. This contradicts classical disconnection accounts of the syndrome stating intact conceptual representations in TSA. Their recovery of language comprehension was associated with activation of a left hemispheric network. Mainly activations of left perilesional pre-frontal regions (RC), left Wernicke's area (RC and HP) or the left posterior middle and inferior temporal cortex (HP) were demonstrated in the TSA patients. The latter findings suggest that in our cases of TSA functional take-over has occurred in regions with related functions ('redundancy recovery') rather than in previously unrelated areas ('vicarious functioning'). Our data support distributed models of conceptual-semantic word processing and multiple left hemispheric representations of closely related functions.     

The response of left temporal cortex to sentences

The meaning of a sentence differs from the sum of the meanings of its constituents. Left anterior temporal cortex responds to sentences more strongly than to unconnected words. We hypothesized that the anterior temporal response to sentences is due to this difference in meaning (compositional semantics). Using positron emission tomography (PET), we studied four experimental conditions (2 x 2 factorial design): In one condition, subjects read normal sentences. In a second condition, they read grammatically correct sentences containing numerous semantic violations (semantically random sentences). In a third condition, we scrambled the word order within the normal sentences, and, in a fourth condition, the word order was scrambled within the semantically random sentences. The left anterior temporal pole responded strongly to sentences compared to scrambled versions of sentences. A similar although weaker response occurred in the left anterior superior temporal sulcus and the left posterior middle temporal gyrus. A subset of voxels within the left anterior temporal pole responded more to semantically random sentences and their scrambled versions than to normal sentences and the corresponding scrambled versions (main effect of semantic randomness). Finally, the grammatical and the semantic factor interacted in a subset of voxels within the anterior temporal pole: Activity was higher when subjects read normal sentences compared to their scrambled versions but not for semantically random sentences compared to their corresponding scrambled versions. The effects of grammar and meaning and, most importantly, the interaction between grammatical and semantic factors are compatible with the hypothesis that the left anterior temporal pole contributes to the composition of sentence meaning.     

Recovery from wernicke's aphasia: A positron emission tomographic study

Changes in the organization of the brain after recovery from aphasia were investigated by measuring increases in regional cerebral blood flow (rCBF) during repetition of pseudowords and during verb generation. Six right-handed patients who had recovered from Wernicke's aphasia caused by an infarction destroying the left posterior perisylvian language zone were compared with 6 healthy, right-handed volunteers. In the control subjects, strong rCBF increases were found in the left hemisphere in the posterior part of the superior and middle temporal gyrus (Wernicke's area), and during the generation task in lateral prefrontal cortex (LPFC) and in inferior frontal gyrus (Broca's area). There were some weak right hemisphere increases in superior temporal gyrus and inferior premotor cortex. In the patients, rCBF increases were preserved in the frontal areas. There was clear right hemisphere activation in superior temporal gyrus and inferior premotor and lateral prefrontal cortices, homotopic to the left hemisphere language zones. Increased left frontal and right perisylvian activity in patients with persisting destruction of Wernicke's area emphasizes redistribution of activity within the framework of a preexisting, parallel processing and bilateral network as the central mechanism in functional reorganization of the language system after stroke.     

Speech production after stroke: the role of the right pars opercularis

Recovery of speech after infarction of the left pars opercularis (POp) may be due to recruitment of homotopic cortex in the right hemisphere. Using positron emission tomography, we investigated activity within left and right POp during everyday propositional speech. We studied seven aphasic patients with left anterior perisylvian infarction which included the POp. We compared their data with two control groups: 12 normal subjects and 7 anterior aphasic patients whose infarcts spared the left POp. During propositional speech, normal subjects activated the left POp, left posterior perisylvian cortex, and a distributed, predominantly left-lateralized, extrasylvian neural network. Importantly, activity in the right POp was reduced relative to a baseline nonspeech condition. In patients with infarction of the left POp, activity in the right POp was reversed: speech activated the right POp above baseline. Patient controls activated the left POp but did not show the normal relative reduction in activity in the right POp. In both patient groups, posterior perisylvian and extrasylvian activations remained unchanged from normal. This result demonstrates that infarction of the left POp is associated with a chronic change in function of the contralateral homotopic cortex during speech.     

Recovery of Semantic Word Processing in Transcortical Sensory Aphasia: a Functional Magnetic Resonance Imaging Study

In a previous functional magnetic resonance imaging (fMRI) study with normal subjects, we demonstrated regions related to conceptual-semantic word processing around the first frontal sulcus (BA 9) and the posterior parietal lobe (BA 7/40) in agreement with several previous reports. We had the possibility, using the same fMRI paradigm, to study two consecutive cases with left middle cerebral artery (MCA) infarction (RC and HP) and lesions affecting either solely the pre-frontal (HP) or both the pre-frontal and posterior parietal part of the network activated in normal subjects (RC). Both patients showed transcortical sensory aphasia (TSA) on acute assessment. This contradicts classical disconnection accounts of the syndrome stating intact conceptual representations in TSA. Their recovery of language comprehension was associated with activation of a left hemispheric network. Mainly activations of left perilesional pre-frontal regions (RC), left Wernicke’s area (RC and HP) or the left posterior middle and inferior temporal cortex (HP) were demonstrated in the TSA patients. The latter findings suggest that in our cases of TSA functional take-over has occurred in regions with related functions (‘redundancy recovery’) rather than in previously unrelated areas (‘vicarious functioning’). Our data support distributed models of conceptual-semantic word processing and multiple left hemispheric representations of closely related functions.     

How would you feel versus how do you think she would feel? A neuroimaging study of perspective-taking with social emotions

Perspective-taking is a complex cognitive process involved in social cognition. This positron emission tomography (PET) study investigated by means of a factorial design the interaction between the emotional and the perspective factors. Participants were asked to adopt either their own (first person) perspective or the (third person) perspective of their mothers in response to situations involving social emotions or to neutral situations. The main effect of third-person versus first-person perspective resulted in hemodynamic increase in the medial part of the superior frontal gyrus, the left superior temporal sulcus, the left temporal pole, the posterior cingulate gyrus, and the right inferior parietal lobe. A cluster in the postcentral gyrus was detected in the reverse comparison. The amygdala was selectively activated when subjects were processing social emotions, both related to self and other. Interaction effects were identified in the left temporal pole and in the right postcentral gyrus. These results support our prediction that the frontopolar, the somatosensory cortex, and the right inferior parietal lobe are crucial in the process of self/other distinction. In addition, this study provides important building blocks in our understanding of social emotion processing and human empathy.     

Sources on the anterior and posterior banks of the central sulcus identified from magnetic somatosensory evoked responses using multistart spatio-temporal localization

A Multi-Start Spatio-Temporal (MSST) multidipole localization algorithm was used to study sources on the anterior and posterior banks of the central sulcus localized from early somatosensory magnetoencephalography (MEG) responses. Electrical stimulation was applied to the right and left median nerves of 8 normal subjects. Two sources, one on the anterior and one on the posterior bank of the central sulcus, were localized from 16 data sets (8 subjects, 2 hemispheres). Compared with the more traditional practice of single-dipole fits to peak latencies, MSST provided more reliable source locations. The temporal dynamics of the anterior and posterior central sulcus sources, obtained using MSST, showed considerable temporal overlap. In some cases, the two sources appeared synchronous. On the other hand, in the traditional single-dipole peak-latency fit approach, there is no time course other than a focal dipole moment activated only at the selected peak latency. The same group of subjects also performed a motor task involving index-finger lifting; the anterior central sulcus source obtained from electrical median nerve stimulation localized to the same or similar region in the primary motor area identified from the finger-lift task. The physiological significance of the anterior central sulcus source is discussed. The findings suggest that one can test the integrity of cortical tissue in the region of primary motor cortex using electrical somatosensory stimulation.     

Cortical substrates for the perception of face actions: an fMRI study of the specificity of activation for seen speech and for meaningless lower-face acts (gurning)

Can the cortical substrates for the perception of face actions be distinguished when the superficial visual qualities of these actions are very similar? Two fMRI experiments are reported. Compared with watching the face at rest, observing silent speech was associated with bilateral activation in a number of temporal cortical regions, including the superior temporal sulcus (STS). Watching face movements of similar extent and duration, but which could not be construed as speech (gurning; Experiment 1b) was not associated with activation of superior temporal cortex to the same extent, especially in the left hemisphere. Instead, the peak focus of the largest cluster of activation was in the posterior part of the inferior temporal gyrus (right, BA 37). Observing silent speech, but not gurning faces, was also associated with bilateral activation of inferior frontal cortex (BA 44 and 45). In a second study, speechreading and observing gurning faces were compared within a single experiment, using stimuli which comprised the speaker's face and torso (and hence a much smaller image of the speaker's face and facial actions). There was again differential engagement of superior temporal cortex which followed the pattern of Experiment 1. These findings suggest that superior temporal gyrus and neighbouring regions are activated bilaterally when subjects view face actions--at different scales--that can be interpreted as speech. This circuitry is not accessed to the same extent by visually similar, but linguistically meaningless actions. However, some temporal regions, such as the posterior part of the right superior temporal sulcus, appear to be common processing sites for processing both seen speech and gurns.     

An fMRI study of simple ethical decision-making

Recent functional neuroimaging studies suggest that ventromedial prefrontal cortex (vmPFC), left posterior superior temporal sulcus (pSTS) and posterior cingulate cortex are engaged during moral decision-making on complex dilemmatic or salient emotional stimuli. In this fMRI study we investigated which of these brain regions are activated during simple ethical decision-making about unambiguous scenarios not containing direct bodily harm or violence. Simple moral decisions compared to semantic decisions resulted in activation of left pSTS and middle temporal gyrus, bilateral temporal poles, left lateral PFC and bilateral vmPFC. These results suggest that pSTS and vmPFC are a common neuronal substrate of decision-making about complex ethical dilemmas, processing material evocative of moral emotions and simple ethical decision-making about scenarios devoid of violence and direct bodily harm.     

Mapping cortical asymmetry and complexity patterns in normal children

This study reports the first comprehensive three-dimensional (3D) maps of cortical patterns in children. Using a novel parametric mesh-based analytic technique applied to high-resolution T1-weighted MRI scans, we examined age (6-16 years) and gender differences in cortical complexity (the fractal dimension or complexity of sulcal/gyral convolutions) and asymmetry of 24 primary cortical sulci in normally developing children (N=24). Three-dimensional models of the cerebral cortex were extracted and major sulci mapped in stereotaxic space. Given the documented age-related changes in frontal lobe functions and several neuroimaging studies that have reported accompanying volumetric changes in these regions, we hypothesized that, with age, we would find continued modifications of the cerebrum in frontal cortex. We also predicted that phylogenetically older regions of the cerebrum, such as olfactory cortex, would be less variable in anatomic location across subjects and with age. Age-related increases in cortical complexity were found in both left and right inferior frontal and left superior frontal regions, possibly indicating an increase in secondary branching with age in these regions. Moreover, a significant increase in the length of the left inferior frontal sulcus and a posterior shifting of the left pre-central sulcus was associated with age. Three-dimensional asymmetry and anatomic variability maps revealed a significant left-greater-than-right asymmetry of the Sylvian fissures and superior temporal sulci, and increased variance in dorsolateral frontal and perisylvian areas relative to ventral regions of the cortex. These results suggest increases in cortical complexity and subtle modifications of sulcal topography of frontal lobe regions, likely reflecting ongoing processes such as myelination and synaptic remodeling that continue into the second decade of life. More studies in a larger sample set and/or longitudinal design are needed to address the issues of normal individual variation and sulcal development.     

Cortical circuits for silent speechreading in deaf and hearing people

This fMRI study explored the functional neural organisation of seen speech in congenitally deaf native signers and hearing non-signers. Both groups showed extensive activation in perisylvian regions for speechreading words compared to viewing the model at rest. In contrast to earlier findings, activation in left middle and posterior portions of superior temporal cortex, including regions within the lateral sulcus and the superior and middle temporal gyri, was greater for deaf than hearing participants. This activation pattern survived covarying for speechreading skill, which was better in deaf than hearing participants. Furthermore, correlational analysis showed that regions of activation related to speechreading skill varied with the hearing status of the observers. Deaf participants showed a positive correlation between speechreading skill and activation in the middle/posterior superior temporal cortex. In hearing participants, however, more posterior and inferior temporal activation (including fusiform and lingual gyri) was positively correlated with speechreading skill. Together, these findings indicate that activation in the left superior temporal regions for silent speechreading can be modulated by both hearing status and speechreading skill.     

Organization of visual inputs to the inferior temporal and posterior parietal cortex in macaques.

It has been proposed that visual information in the extrastriate cortex is conveyed along 2 major processing pathways, a "dorsal" pathway directed to the posterior parietal cortex, underlying spatial vision, and a "ventral" pathway directed to the inferior temporal cortex, underlying object vision. To determine the relative distributions of cells projecting to the 2 pathways, we injected the posterior parietal and inferior temporal cortex with different fluorescent tracers in 5 rhesus monkeys. The parietal injections included the ventral intraparietal (VIP) and lateral intraparietal (LIP) areas, and the temporal injections included the lateral portions of cytoarchitectonic areas TE and TEO. There was a remarkable segregation of cells projecting to the 2 systems. Inputs to the parietal cortex tended to arise either from areas that have been implicated in spatial or motion analysis or from peripheral field representations in the prestriate cortex. By contrast, inputs to the temporal cortex tended to arise from areas that have been implicated in form and color analysis or from central field representations. Cells projecting to the parietal cortex were found in visual area 2 (V2), but only in the far peripheral representations of both the upper and lower visual field. Likewise, labeled cells found in visual areas 3 (V3) and 4 (V4) were densest in their peripheral representations. Heavy accumulations of labeled cells were found in the dorsal parieto-occipital cortex, including the parieto-occipital (PO) area, part A of V3 (V3A), and the dorsal prelunate area (DP). In the superior temporal sulcus, cells were found within several motion-sensitive areas, including the middle temporal area (MT), the medial superior temporal area (MST), the fundus of the superior temporal area (FST), and the superior temporal polysensory area (STP), as well as within anterior portions of the sulcus whose organization is as yet poorly defined. Cells projecting to areas TE and TEO in the temporal cortex were located within cytoarchitectonic area TG at the temporal pole and cytoarchitectonic areas TF and TH on the parahippocampal gyrus, as well as in noninjected portions of area TE buried within the superior temporal sulcus. In the prestriate cortex, labeled cells were found in V2, V3, and V4, but, in contrast to the loci labeled after parietal injections, those labeled after temporal injections were concentrated in the foveal or central field representations. Although few double-labeled cells were seen, 2 regions containing intermingled parietal- and temporal-projection cells were area V4 and the cortex at the bottom of the anterior superior temporal sulcus.(ABSTRACT TRUNCATED AT 400 WORDS)     

Neuronal loss correlates with but exceeds neurofibrillary tangles in Alzheimer's disease

To assess the relationship between dementia, neuronal loss, and neuropathological findings in Alzheimer's disease (AD), we counted the number of neurons, senile plaques, and neurofibrillary tangles in a high-order association cortex. We studied the superior temporal sulcus of 34 individuals with AD and 17 nondemented control subjects, using statistically unbiased, stereological counting techniques. The number of superior temporal sulcus neurons in nondemented control subjects was stable across the sixth to ninth decades. In AD, more than 50% of the neurons were lost. Both neuronal loss and neurofibrillary tangles increased in parallel with the duration and severity of illness, but the amount of neuronal loss exceeded by manyfold the amount of neurofibrillary tangles accumulated. In contrast to the correlation between neurofibrillary tangels and neuronal loss, the number of senile plaques and the percentage of the superior temporal sulcus that was covered by Aβ (amyloid burden) were not related to neuronal loss, number of neurofibrillary tangles, or duration of disease. Neither the amount nor the rate of neuronal loss in the superior temporal sulcus in AD correlated with apolipoprotein E genotype. These data suggest that neuronal loss in association areas such as the superior temporal sulcus contributes directly to cognitive impairment in AD.     

Retrieving meaning after temporal lobe infarction: the role of the basal language area

During speech comprehension the auditory association cortex in the superior temporal cortex is involved in perceptual analysis of the speech signal, whereas the basal language area in the inferior temporal cortex mediates access to word meaning. Disruption of the interaction between the superior and inferior temporal cortices is one factor that may determine recovery from aphasic stroke. We used positron emission tomography to investigate semantic processing within inferior temporal cortex in control subjects and after infarction involving the superior temporal cortex. In the control group, semantic decision making on clear speech activated both anterior fusiform gyri. Chronic aphasic patients were impaired at the task and demonstrated reduced activation within the left anterior fusiform gyrus. A similar pattern of impaired performance and reduced left anterior fusiform gyrus activation was observed when control subjects heard perceptually degraded speech. Performance in both groups predicted activity in the right anterior fusiform gyrus and the temporal poles, where accuracy linearly correlated with activity. These results demonstrate that the function of the basal language area is sensitive to changes in the quality of perceptual input. In addition, different profiles of response observed in each hemisphere suggest distinct contributions of both left and right inferior temporal cortices to the semantic processing of speech.     

Neocortical thinning in "benign" mesial temporal lobe epilepsy

Purpose : In refractory mesial temporal lobe epilepsy (MTLE) extrahippocampal and neocortical abnormalities have been described in patients with or without mesial temporal sclerosis (MTS). Recently we observed gray matter reductions in regions outside the hippocampus in benign MTLE with or without MTS. Cortical thickness has been proposed as a viable methodologic alternative for assessment of neuropathologic changes in extratemporal regions. Herein, we aimed to use this technique to describe cortical abnormalities in patients with benign TLE. Methods : Whole‐brain cortical thickness analysis (FreeSurfer) was performed in 32 unrelated patients with benign TLE [16 patients with signs of MTS on magnetic resonance imaging (MRI), pMTLE; 16 without, nMTLE] and 44 healthy controls. Key Findings : In the pMTLE group, the most significant thinning was found in the sensorimotor cortex bilaterally but was more extensive in the left hemisphere (false discovery rate, p < 0.05). Other areas were localized in the occipital cortex, left supramarginal gyrus, left superior parietal gyrus, left paracentral sulcus, left inferior/middle/superior frontal gyrus, left inferior frontal sulcus, right cingulate cortex, right superior frontal gyrus, right inferior parietal gyrus, right fusiform gyrus, and cuneus/precuneus. In the nMTLE, a similar neurodegenerative pattern was detected, although not surviving correction for multiple comparisons. Direct comparison between pMTLE and nMTLE did not reveal significant changes. Significance : Patients with either benign pMTLE or nMTLE showed comparable cortical thinning, mainly confined to the sensorimotor cortex. This finding that is not appreciated on routine MRI supports the hypothesis that similar to refractory MTLE, even in benign MTLE, pathology in neocortical regions maybe implicated in the pathophysiology of this syndrome.     

Serotonin modulation of cerebral glucose metabolism measured with positron emission tomography (PET) in human subjects

To develop a method to measure the dynamic response of the serotonin system in vivo, the effects of intravenously administered citalopram (the most selective of the serotonin reuptake inhibitors) on cerebral glucose metabolism were evaluated. Cerebral glucose metabolism was measured with positron emission tomography (PET) in 14 normal subjects scanned after administration of saline placebo and citalopram administered on 2 separate days. Citalopram administration resulted in a decrease in metabolism in the right anterior cingulate gyrus (BA 24/32), right superior (BA 9) and right middle frontal gyrus (BA 6), right parietal cortex (precuneus), right superior occipital gyrus, left thalamus, and right cerebellum. Increased metabolism was observed in the left superior temporal gyrus and left occipital cortex. Alterations in metabolism by acute citalopram administration involved the heteromodal association cortices that also show metabolic alterations in patients with geriatric depression and overlap with the regions affected by antidepressant treatment. Future studies will evaluate how the acute metabolic response to citalopram relates to the metabolic response after chronic treatment in patients with geriatric depression.     

Spectro-temporal processing during speech perception involves left posterior auditory cortex

This functional magnetic resonance imaging study investigates the neural underpinnings of spectro-temporal integration during speech perception. Participants performed an auditory discrimination task on a set of sine-wave analogues that could be perceived as either nonspeech or speech. Behavioural results revealed a difference in the processing mode; spectro-temporal integration occurred during speech perception, but not when stimuli were perceived as nonspeech. In terms of neuroimaging, we observed an activation increase in the left posterior primary and secondary auditory cortex, namely Heschl's gyrus and planum temporale encroaching onto the superior temporal sulcus, reflecting a shift from auditory to speech perception. This finding demonstrates that the left posterior superior temporal lobe is essential for spectro-temporal processing during speech perception.     

Tactile-visual integration in the posterior parietal cortex: a functional magnetic resonance imaging study

To explore the neural substrates of visual-tactile crossmodal integration during motion direction discrimination, we conducted functional magnetic resonance imaging with 15 subjects. We initially performed independent unimodal visual and tactile experiments involving motion direction matching tasks. Visual motion discrimination activated the occipital cortex bilaterally, extending to the posterior portion of the superior parietal lobule, and the dorsal and ventral premotor cortex. Tactile motion direction discrimination activated the bilateral parieto-premotor cortices. The left superior parietal lobule, intraparietal sulcus, bilateral premotor cortices and right cerebellum were activated during both visual and tactile motion discrimination. Tactile discrimination deactivated the visual cortex including the middle temporal/V5 area. To identify the crossmodal interference of the neural activities in both the unimodal and the multimodal areas, tactile and visual crossmodal experiments with event-related designs were also performed by the same subjects who performed crossmodal tactile-visual tasks or intramodal tactile-tactile and visual-visual matching tasks within the same session. The activities detected during intramodal tasks in the visual regions (including the middle temporal/V5 area) and the tactile regions were suppressed during crossmodal conditions compared with intramodal conditions. Within the polymodal areas, the left superior parietal lobule and the premotor areas were activated by crossmodal tasks. The left superior parietal lobule was more prominently activated under congruent event conditions than under incongruent conditions. These findings suggest that a reciprocal and competitive association between the unimodal and polymodal areas underlies the interaction between motion direction-related signals received simultaneously from different sensory modalities.