Secondary Somatosensory Regions Research Articles

Alterations in somatosensory, visual and auditory pathways in amyotrophic lateral sclerosis: an under-recognised facet of ALS.

While amyotrophic lateral sclerosis (ALS) is widely recognised as a multi-network disorder with extensive frontotemporal and cerebellar involvement, sensory dysfunction is relatively under evaluated. Subtle sensory deficits have been sporadically reported, but there is a prevailing notion that sensory pathways may be relatively spared in ALS. In a prospective neuroimaging study we have systematically evaluated cerebral grey and white matter structures involved in the processing, relaying and mediation of sensory information. Twenty two C9orf72 positive ALS patients (C9+ ALS), 138 C9orf72 negative ALS patients (C9- ALS) and 127 healthy controls were included. Widespread cortical alterations were observed in C9+ ALS including both primary and secondary somatosensory regions. In C9- ALS, cortical thickness reductions were observed in the postcentral gyrus. Thalamic nuclei relaying somatosensory information as well as the medial and lateral geniculate nuclei exhibited volume reductions. Diffusivity indices revealed posterior thalamic radiation pathology and a trend of left medial lemniscus degeneration was also observed in C9- ALS (p = 0.054). Our radiology data confirm the degeneration of somatosensory, visual and auditory pathways in ALS, which is more marked in GGGGCC hexanucleotide repeat expansion carriers. In contrast to the overwhelming focus on motor system degeneration and frontotemporal dysfunction in recent research studies, our findings confirm that sensory circuits are also affected in ALS. The involvement of somatosensory, auditory and visual pathways in ALS may have important clinical ramifications which are easily overlooked in the context of unremitting motor decline. Subtle sensory deficits may exacerbate mobility, contribute to fall risk, impair dexterity, and worsen bulbar dysfunction, therefore comprehensive sensory testing should also be performed as part of the clinical assessments in ALS.

Task-dependent cortical activations during selective attention to audiovisual speech

Selective listening to speech depends on widespread networks of the brain, but how the involvement of different neural systems in speech processing is affected by factors such as the task performed by a listener and speech intelligibility remains poorly understood. We used functional magnetic resonance imaging to systematically examine the effects that performing different tasks has on neural activations during selective attention to continuous audiovisual speech in the presence of task-irrelevant speech. Participants viewed audiovisual dialogues and attended either to the semantic or the phonological content of speech, or ignored speech altogether and performed a visual control task. The tasks were factorially combined with good and poor auditory and visual speech qualities. Selective attention to speech engaged superior temporal regions and the left inferior frontal gyrus regardless of the task. Frontoparietal regions implicated in selective auditory attention to simple sounds (e.g., tones, syllables) were not engaged by the semantic task, suggesting that this network may not be not as crucial when attending to continuous speech. The medial orbitofrontal cortex, implicated in social cognition, was most activated by the semantic task. Activity levels during the phonological task in the left prefrontal, premotor, and secondary somatosensory regions had a distinct temporal profile as well as the highest overall activity, possibly relating to the role of the dorsal speech processing stream in sub-lexical processing. Our results demonstrate that the task type influences neural activations during selective attention to speech, and emphasize the importance of ecologically valid experimental designs.

Lower limb amputees undergo long-distance plasticity in sensorimotor functional connectivity

Amputation in adults is associated with an extensive remapping of cortical topography in primary and secondary sensorimotor areas. Here, we used tactile residual limb stimulation and 3T functional magnetic resonance imaging in humans to investigate functional connectivity changes in the sensorimotor network of patients with long-term lower limb traumatic amputations with phantom sensation, but without pain. We found a pronounced reduction of inter-hemispheric functional connectivity between homologous sensorimotor cortical regions in amputees, including the primary (S1) and secondary (S2) somatosensory areas, and primary (M1) and secondary (M2) motor areas. We additionally observed an intra-hemispheric increased functional connectivity between primary and secondary somatosensory regions, and between the primary and premotor areas, contralateral to amputation. These functional connectivity changes in specialized small-scale sensory-motor networks improve our understanding of the functional impact of lower limb amputation in the brain. Our findings in a selective group of patients with phantom limb sensations, but without pain suggest that disinhibition of neural inputs following traumatic limb amputation disrupts sensorimotor topology, unbalancing functional brain network organization. These findings step up the description of brain plasticity related with phantom sensations by showing that pain is not critical for sensorimotor network changes after peripheral injury.

Activation of Bilateral Secondary Somatosensory Cortex With Right Hand Touch Stimulation: A Meta-Analysis of Functional Neuroimaging Studies.

Background: Brain regions involved in processing somatosensory information have been well documented through lesion, post-mortem, animal, and more recently, structural and functional neuroimaging studies. Functional neuroimaging studies characterize brain activation related to somatosensory processing; yet a meta-analysis synthesis of these findings is currently lacking and in-depth knowledge of the regions involved in somatosensory-related tasks may also be confounded by motor influences.Objectives: Our Activation Likelihood Estimate (ALE) meta-analysis sought to quantify brain regions that are involved in the tactile processing of the right (RH) and left hands (LH) separately, with the exclusion of motor related activity.Methods: The majority of studies (n = 41) measured activation associated with RH tactile stimulation. RH activation studies were grouped into those which conducted whole-brain analyses (n = 29) and those which examined specific regions of interest (ROI; n = 12). Few studies examined LH activation, though all were whole-brain studies (N = 7).Results: Meta-analysis of brain activation associated with RH tactile stimulation (whole-brain studies) revealed large clusters of activation in the left primary somatosensory cortex (S1) and bilaterally in the secondary somatosensory cortex (S2; including parietal operculum) and supramarginal gyrus (SMG), as well as the left anterior cingulate. Comparison between findings from RH whole-brain and ROI studies revealed activation as expected, but restricted primarily to S1 and S2 regions. Further, preliminary analyses of LH stimulation studies only, revealed two small clusters within the right S1 and S2 regions, likely limited due to the small number of studies. Contrast analyses revealed the one area of overlap for RH and LH, was right secondary somatosensory region.Conclusions: Findings from the whole-brain meta-analysis of right hand tactile stimulation emphasize the importance of taking into consideration bilateral activation, particularly in secondary somatosensory cortex. Further, the right parietal operculum/S2 region was commonly activated for right and left hand tactile stimulation, suggesting a lateralized pattern of somatosensory activation in right secondary somatosensory region. Implications for further research and for possible differences in right and left hemispheric stroke lesions are discussed.

Cognition sociale dans la schizophrénie et les troubles du spectre de l’autisme : points de convergences et différences fonctionnelles

IntroductionSchizophrenia and autistic spectrum disorder (ASD) are two neurodevelopmental disorders that have different symptom presentations, ages of onset and developmental courses. Both schizophrenia and ASD are characterized by marked deficit in communication, social interactions, affects and emotions. Social cognitive impairments in ASD and schizophrenia were demonstrated separately in both disorders. It was reported that these impairments have direct relation with social deficits of both disorders. The apparent similarity between social cognition impairments in ASD and schizophrenia highlights questions about the existence of common or different neurocognitive mechanisms related to social dysfunctions. In order to examine these questions, the present article provides a comprehensive review of all published studies which directly compare individuals with ASD and schizophrenia on the same cognitive tasks of social cognition. MethodsThe article search was made on Pubmed, PsycInfo and ScienceDirect, with the items: “autism”, “Asperger syndrome”, “schizophrenia”, “social cognition”, “theory of mind”, “emotional processing”, “social perception”, “attributions style”. All published studies which compared individuals with ASD and schizophrenia, (diagnosed according to DSM-IV (APA, 1994) criteria and IQ≥70), included control group were considered. The cognitive tasks were categorized according to four domains of social cognition defined by SCOPE (Pinkham et al., 2013): theory of mind (ToM), emotional processing (EP), social perception (SP) and attributional style/bias. The results were analyzed in terms of performances, cognitive profile and patterns of neural activations. Twenty-one published studies and two meta-analytic reviews were analyzed. ResultsCognitive performance analysis confirms the convergence of abnormalities of people with autism and people with schizophrenia on 1st and 2nd order theory of mind, emotion processing and social perception. Quantitative results show reduced performance in ASD compared to SZ and Ct groups. Differences were observed between ASD and SZ regarding social situation comprehension, visual orientation and visuospatial exploration strategies, and attributional style highlighting different strategies on intentional process. Brain imaging studies show that people with autism present a reduced cerebral activity in several key regions of theory of mind (cingulate regions, superior temporal sulcus, paracentral lobule), and emotional treatment (primary and secondary somatosensory regions), while people with SZ exhibit an inappropriate increased activity in these regions. ConclusionThe present revue of the studies which directly compare individuals with ASD and schizophrenia on different domains of social cognition indicates that both disorders exhibit differences and similarities with regard to behavioral performances. Results in neuroimaging indicate different neurocognitive mechanisms underlie apparently similar social-cognitive impairments. Further studies are needed to better explore and describe divergent neurocognitive mechanisms in ASD and schizophrenia in order to provide treatment and remediation methods that take into account the specificities of neurocognitive processes in the two disorders.

Multisensory coding in the multiple-demand regions: vibrotactile task information is coded in frontoparietal cortex.

At any given moment, our brains receive input from multiple senses. Successful behavior depends on our ability to prioritize the most important information and ignore the rest. A multiple-demand (MD) network of frontal and parietal regions is thought to support this process by adjusting to code information that is currently relevant (Duncan 2010). Accordingly, the network is proposed to encode a range of different types of information, including perceptual stimuli, task rules, and responses, as needed for the current cognitive operation. However, most MD research has used visual tasks, leaving limited information about whether these regions encode other sensory domains. We used multivoxel pattern analysis (MVPA) of functional magnetic resonance imaging (fMRI) data to test whether the MD regions code the details of somatosensory stimuli, in addition to tactile-motor response transformation rules and button-press responses. Participants performed a stimulus-response task in which they discriminated between two possible vibrotactile frequencies and applied a stimulus-response transformation rule to generate a button-press response. For MD regions, we found significant coding of tactile stimulus, rule, and response. Primary and secondary somatosensory regions encoded the tactile stimuli and the button-press responses but did not represent task rules. Our findings provide evidence that MD regions can code nonvisual somatosensory task information, commensurate with a domain-general role in cognitive control.NEW & NOTEWORTHY How does the brain encode the breadth of information from our senses and use this to produce goal-directed behavior? A network of frontoparietal multiple-demand (MD) regions is implicated but has been studied almost exclusively in the context of visual tasks. We used multivariate pattern analysis of fMRI data to show that these regions encode tactile stimulus information, rules, and responses. This provides evidence for a domain-general role of the MD network in cognitive control.

Functional and Quantitative MRI Mapping of Somatomotor Representations of Human Supralaryngeal Vocal Tract.

Speech articulation requires precise control of and coordination between the effectors of the vocal tract (e.g., lips, tongue, soft palate, and larynx). However, it is unclear how the cortex represents movements of and contact between these effectors during speech, or how these cortical responses relate to inter-regional anatomical borders. Here, we used phase-encoded fMRI to map somatomotor representations of speech articulations. Phonetically trained participants produced speech phones, progressing from front (bilabial) to back (glottal) place of articulation. Maps of cortical myelin proxies (R1 = 1/T1) further allowed us to situate functional maps with respect to anatomical borders of motor and somatosensory regions. Across participants, we found a consistent topological map of place of articulation, spanning the central sulcus and primary motor and somatosensory areas, that moved from lateral to inferior as place of articulation progressed from front to back. Phones produced at velar and glottal places of articulation activated the inferior aspect of the central sulcus, but with considerable across-subject variability. R1 maps for a subset of participants revealed that articulator maps extended posteriorly into secondary somatosensory regions. These results show consistent topological organization of cortical representations of the vocal apparatus in the context of speech behavior.

Brain activity for visual judgment of lifted weight

It is well established that humans can recognize high-level aspects from point-light biological motion, such as gender and mood. If the task is to judge the manipulated weight we expected that sensorimotor regions should be recruited in the brain. Moreover, we have recently shown that chronic pain in a limb that is involved in the presented movement disturbs the weight judgment. We therefore hypothesized that some cortical regions usually activated during the processing of pain will also be activated while viewing point-light biological motion with the instruction to judge the manipulated weights. We investigated point-light biological motion of two types of movements performed with different weights in a blocked fMRI experiment in healthy subjects. In line with our a priori hypothesis, we found strong activity in the regions known as the neuromatrix of pain, such as the anterior cingulate (ACC), insula, as well as primary and secondary somatosensory regions. We also found activation in the occipital and temporal regions that are typical for biological motion, as well as regions in the cerebellum and prefrontal cortex. The activation of the somatosensory regions probably serves the judgment of the biological motion stimuli. Activation of the anterior cingulate and the insula might be explained by their role in the integration of behaviorally relevant information. Alternatively, these structures are known to be involved in the processing of nociceptive information and pain. So it seems possible that the interference between judgment of weights and perception of pain in chronic pain patients occurs in the somatosensory areas, anterior cingulate and/or insula. This finding provides important information as to the underlying mechanisms used for the weight judgment task, but also why chronic pain interferes with this task.

A Neural Link Between Feeling and Hearing

Hearing and feeling both rely upon the transduction of physical events into frequency-based neural codes, suggesting that the auditory system may be intimately related to the somatosensory system. Here, we provide evidence that the neural substrates for audition and somatosensation are anatomically linked. Using diffusion tensor imaging with both deterministic and probabilistic tractography to measure white matter connectivity, we show that there are extensive ipsilateral connections between the primary auditory cortex and the primary and secondary somatosensory regions in the human cerebral cortex. We further show that these cross-modal connections are exaggerated between the auditory and secondary somatosensory cortex in the lesioned hemisphere of a patient (SR) with acquired auditory-tactile synesthesia, in whom sounds alone produce bodily sensations. These results provide an anatomical basis for multisensory interactions between audition and somatosensation and suggest that cross-talk between these regions may explain why some sounds, such as nails screeching down a chalkboard or an audible mosquito, can induce feelings of touch, especially on the contralesional body surface of patient SR.

A neural link between feeling and hearing

Hearing and feeling both rely upon the transduction of physical events into frequency-based neural codes, suggesting that the auditory system may be intimately related to the somatosensory system. In this study, we provide evidence that the neural substrates for audition and somatosensation are anatomically linked. Using diffusion tensor imaging with both deterministic and probabilistic tractography to measure white matter connectivity, we show that there are extensive connections between the primary auditory cortex and the primary and secondary somatosensory regions in human cerebral cortex. We further show that these cross-connections are diminished between auditory and primary somatosensory cortex and exaggerated between auditory and secondary somatosensory cortex in the lesioned hemisphere of a patient (SR) with acquired auditory-tactile synesthesia, in whom sounds alone produce bodily sensations. These results provide an anatomical basis for multisensory interactions between audition and somatosensation and suggest that cross-talk between these regions may explain why some sounds, such as nails screeching down a chalkboard or an audible mosquito, can induce feelings of touch, especially on the left half of patient SR.

Increasing the efficiency of neonatal MEG measurements by alternating auditory and tactile stimulation

Objective To evaluate the possible effect of intervening auditory stimulation on somatosensory evoked magnetic fields in newborns. Methods We recorded auditory and tactile evoked responses with magnetoencephalography (MEG) from two groups of healthy newborns. One group ( n = 11) received only tactile stimuli to the index finger, the other ( n = 11) received alternating tactile and auditory (vowel [a:] with 300-ms duration) stimuli. The interval between subsequent tactile stimuli was always 2 s. We analyzed the equivalent current dipoles (ECDs) of the main auditory and somatosensory responses. Results The ECDs of the tactile responses agreed with activation of the primary somatosensory cortex at ∼60 ms and the secondary somatosensory region at ∼200 ms. The source of the auditory response (∼250 ms) was clearly distinct from those to tactile stimulation and in line with auditory cortex activation. The intervening auditory stimulation did not affect the strength, latency, or location of the ECDs of the tactile responses. Conclusions Auditory and tactile MEG responses from newborns can be obtained in one measurement session. Significance The alternating stimulation can be used to shorten the total measurement time and/or to improve the signal to noise ratio by collecting more data.

Quantification of the Effects of Transcutaneous Electrical Nerve Stimulation With Functional Magnetic Resonance Imaging: A Double-Blind Randomized Placebo-Controlled Study

Kara M, Özçakar L, Gökçay D, Özçelik E, Yörübulut M, Güneri S, Kaymak B, Akıncı A, Çetin A. Quantification of the effects of transcutaneous electrical nerve stimulation with functional magnetic resonance imaging: a double-blind randomized placebo-controlled study. Objective To evaluate the effects of transcutaneous electric nerve stimulation (TENS) by using functional magnetic resonance imaging (fMRI) in patients with carpal tunnel syndrome (CTS). Design Randomized controlled trial. Settings University medical center and an outpatient imaging center. Participants Female patients with CTS (n=20) were randomized into 2 groups receiving either TENS (n=10) or sham TENS (n=10). In both groups, an initial baseline fMRI session was performed via stimulating digits 2, 5, and 3 in turn, 1 scan run for each. TENS versus sham TENS treatment was given, and a repeat imaging was performed starting 20 minutes after the treatment as follows: second finger on the 20th minute, fifth finger on the 25th minute (ulnar nerve innervated control finger), and third finger on the 30th min. Interventions Not applicable. Main Outcome Measure Differences in fMRI activation between the 2 groups were evaluated. Results Our results demonstrated that 20 to 25 minutes after TENS treatment—but not in the sham TENS group—a significant fMRI signal decrease for digit 2 (post-TENS vs baseline) was observed in the secondary somatosensory regions, ipsilateral primary motor cortex (M1), contralateral supplementary motor cortex (SMA), contralateral parahippocampal gyrus, contralateral lingual gyrus, and bilateral superior temporal gyrus. Measurements on the 25th to 30th minutes for digit 5 were similar between the groups, with presence of activities in areas other than generally activated regions because of painful stimuli. Thirty to 35 minutes after TENS treatment, a significant fMRI signal decrease for digit 3 was detected in the contralateral M1 and contralateral SMA only in the TENS group. Conclusions Our findings showed that TENS treatment significantly decreased the pain-related cortical activations caused by stimulation of the median nerve–innervated fingers up to 35 minutes after treatment.

Activation of Primary and Secondary Somatosensory Regions Following Tactile Stimulation of the Face

Since the work of Penfield & Rasmussen it is well established that the human primary somatosensory cortex is organized somatotopically. However, the order of the representation of the face is still a matter of discussion, i.e., it is yet unclear whether the face is represented upside-down or vice versa in the somatosensory cortex. In a functional magnetic resonance imaging study (n = 30), tactile stimuli to three different locations on each side of the face were applied using a pneumatic device. Locations of stimulation corresponded to the three branches of the trigeminal nerve (forehead, cheek, chin). To determine the representation of the face on primary and secondary somatosensory cortices, peak coordinates within these regions were analyzed subjectwise. Contralateral activation of the primary somatosensory cortex following tactile stimulation of the face was found, whereas the secondary somatosensory cortices were activated bilaterally. However, differences between activation coordinates of different tactile stimuli applied to one side of the face were not statistically significant. Tactile stimulation of the face leads to contralateral activation of primary and bilateral activation of secondary somatosensory cortices. Using the authors' methodological approach it was not possible to detect a somatotopic organization related to different facial areas.

Hypothalamus, sexual arousal and psychosexual identity in human males: a functional magnetic resonance imaging study

In a recent functional magnetic resonance imaging study, a complex neural circuit was shown to be involved in human males during sexual arousal [A. Ferretti et al. (2005) Neuroimage, 26, 1086]. At group level, there was a specific correlation between penile erection and activations in anterior cingulate, insula, amygdala, hypothalamus and secondary somatosensory regions. However, it is well known that there are remarkable inter-individual differences in the psychological view and attitude to sex of human males. Therefore, a crucial issue is the relationship among cerebral responses, sexual arousal and psychosexual identity at individual level. To address this issue, 18 healthy male subjects were recruited. Their deep sexual identity (DSI) was assessed following the construct revalidation by M. Olivetti Belardinelli [(1994) Sci. Contrib. Gen. Psychol., 11, 131] of the Franck drawing completion test, a projective test providing, according to this revalidation, quantitative scores on 'accordance/non-accordance' between self-reported and psychological sexual identity. Cerebral activity was evaluated by means of functional magnetic resonance imaging during hard-core erotic movies and sport movies. Results showed a statistically significant positive correlation between the blood oxygen level-dependent signal in bilateral hypothalamus and the Franck drawing completion test score during erotic movies. The higher the blood oxygen level-dependent activation in bilateral hypothalamus, the higher the male DSI profile. These results suggest that, in male subjects, inter-individual differences in the DSI are strongly correlated with blood flow to the bilateral hypothalamus, a dimorphic brain region deeply implicated in instinctual drives including reproduction.

Neuronal correlates of gastric pain induced by fundus distension: a 3T‐fMRI study

Visceral hypersensitivity in gastric fundus is a possible pathogenesis for functional dyspepsia. The cortical representation of gastric fundus is still unclear. Growing evidence shows that the insula, but not the primary or secondary somatosensory region (SI or SII), may be the cortical target for visceral pain. Animal studies have also demonstrated that amygdala plays an important role in processing visceral pain. We used fMRI to study central projection of stomach pain from fundus balloon distension. We also tested the hypothesis that there will be neither S1 nor S2 activation, but amygdala activation with the fundus distension. A 3T-fMRI was performed on 10 healthy subjects during baseline, fullness (12.7 +/- 0.6 mmHg) and moderate gastric pain (17.0 +/- 0.8 mmHg). fMRI signal was modelled by convolving the predetermined psychophysical response. Statistical comparisons were performed between conditions on a group level. Gastric pain activated a wide range of cortical and subcortical structures, including thalamus and insula, anterior and posterior cingulate cortices, basal ganglia, caudate nuclei, amygdala, brain stem, cerebellum and prefrontal cortex (P < 0.001). A subset of these neuronal substrates was engaged in the central processing of fullness sensation. SI and SII were not activated during the fundus stimulation. In conclusion, the constellation of neuronal structures activated by fundus distension overlaps the pain matrices induced musculocutaneous pain, with the exception of the absence of SI or SII activation. This may account for the vague nature of visceral sensation/pain. Our data also confirms that the insula and amygdala may act as the central role in visceral sensation/pain, as well as in the proposed sensory-limbic model of learning and memory of pain.

Tactile attention tasks enhance activation in somatosensory regions of parietal cortex: a positron emission tomography study.

We used positron emission tomography to study cortical regions mediating tactile attention. Cues selectively directed subjects to attend to the roughness or duration of contact with embossed gratings that rubbed against a single fingertip with controlled speed and force. The task required discriminating between paired gratings that differed in tactile features of roughness and/or length. For different blocks of trials, cues directed attention to one tactile feature or indicated a divided attention strategy to a change in either feature. All attention conditions unambiguously activated several somatosensory foci in the parietal cortex, including somatotopically appropriate portions of the primary somatosensory cortex in the postcentral gyrus (S1) and the secondary somatosensory region (S2) within parietal opercular regions. There was no evidence for separate processing foci for selective and divided attention strategies, or for selectively attending to roughness versus stimulus duration. We observed a greater magnitude blood flow change in S2 versus S1 during attention tasks, which suggests that S2 might actually influence S1 activity. Despite these differences, modulation of S1 and S2 supports concepts of early selection in tactile attention. There were also examples of non-sensory foci in frontal cortex, anterior cingulate gyrus and bilateral superior parietal regions at the fundus of the postcentral sulcus. Posterior parietal regions observed in this study did not overlap foci seen in studies of visual attention. Thus, the posterior parietal region may be subdivided into modality-specific subregions, each of which processes information needed to attend to a specific modality. These non-sensory areas may constitute a network that provides a source of modulating influences on the earlier stage, sensory areas.

A Comparative fMRI Study of Cortical Representations for Thermal Painful, Vibrotactile, and Motor Performance Tasks

Cortical activity due to a thermal painful stimulus applied to the right hand was studied in the middle third of the contralateral brain and compared to activations for vibrotactile and motor tasks using the same body part, in nine normal subjects. Cortical activity was demonstrated utilizing multislice echo-planar functional magnetic resonance imaging (fMRI) and a surface coil. The cortical activity was analyzed based upon individual subject activity maps and on group-averaged activity maps. The results show significant differences in activations across the three tasks and the cortical areas studied. The study indicates that fMRI enables examination of cortical networks subserving pain perception at an anatomical detail not available with other brain imaging techniques and shows that this cortical network underlying pain perception shares components with the networks underlying touch perception and motor execution. However, the thermal pain perception network also has components that are unique to this percept. The uniquely activated areas were in the secondary somatosensory region, insula, and posterior cingulate cortex. The posterior cingulate cortex activity was in a region that, in the monkey, receives nociceptive inputs from posterior thalamic medial and lateral nuclei that in turn are targets for spinothalamic terminations. Discrete subdivisions of the primary somatosensory and motor cortical areas were also activated in the thermal pain task, showing region-dependent differences in the extent of overlap with the other two tasks. Within the primary motor cortex, a hand region was preferentially active in the task in which the stimulus was painful heat. In the primary somatosensory cortex most activity in the painful heat task was localized to area 1, where the motor and vibratory task activities were also coincident. The study also indicates that the functional connectivity across multiple cortical regions reorganizes dynamically with each task.

Cortical afferents and efferents of monkey postarcuate area: an anatomical and electrophysiological study.

A study has been made of the corticocortical efferent and afferent connections of the posterior bank of the arcuate sulcus in the macaque monkey. The distribution of efferent projections to the primary motor cortex (MI) was studied by injecting three different fluorescent retrograde tracers into separate regions of MI. The resultant labeling showed a discrete and topographically organized projection: neurons lying below the inferior limb of the arcuate sulcus project into the MI face area, while neurons located in the posterior bank of the inferior limb of the arcuate sulcus and in the arcuate spur region project into the MI hand area. These findings were confirmed electrophysiologically by demonstrating that postarcuate neurons could only be activated antidromically by stimulation within restricted regions of MI. HRP injections within postarcuate cortex indicated that afferents to this region arise from a number of cortical areas. However, the largest numbers of labeled neurons were found in the posterior parietal cortex (area 7b; PF) and in the secondary somatosensory region (SII). Neurons in both 7b (PF) and SII could be antidromically activated by postarcuate stimulation. It was further shown that stimulation of area 7b (PF) gives rise to short-latency synaptic responses in postarcuate neurons, including some neurons with identified projections to MI. The results are discussed in relation to the possible function of the postarcuate region of the premotor cortex in the sensory guidance of movement.