Area 3b Research Articles

Microstimulation and architectonics of frontoparietal cortex in common marmosets (Callithrix jacchus)

We investigated the organization of frontoparietal cortex in the common marmoset (Callithrix jacchus) by using intracortical microstimulation and an architectonic analysis. Primary motor cortex (M1) was identified as an area that evoked visible movements at low levels of electric current and had a full body representation of the contralateral musculature. Primary motor cortex represented the contralateral body from hindlimb to face in a mediolateral sequence, with individual movements such as jaw and wrist represented in multiple nearby locations. Primary motor cortex was coextensive with an agranular area of cortex marked by a distinct layer V of large pyramidal cells that gradually decreased in size toward the rostral portion of the area and was more homogenous in appearance than other New World primates. In addition to M1, stimulation also evoked movements from several other areas of frontoparietal cortex. Caudal to primary motor cortex, area 3a was identified as a thin strip of cortex where movements could be evoked at thresholds similar to those in M1. Rostral to primary motor cortex, supplementary motor cortex and premotor areas responded to higher stimulation currents and had smaller layer V pyramidal cells. Other areas evoking movements included primary somatosensory cortex (area 3b), two lateral somatosensory areas (areas PV and S2), and a caudal somatosensory area. Our results suggest that frontoparietal cortex in marmosets is organized in a similar fashion to that of other New World primates.

Co-activation patterns in somatosensory areas: A meta-analysis study

Event Abstract Back to Event Co-activation patterns in somatosensory areas: A meta-analysis study Lars Forsberg1* and Per Roland1 1 Karolinska Institute, Sweden Introduction: NeuroGenerator is a project that generates statistical image databases from PET and fMRI studies (Roland et al. 2001). This is done by processing the raw data in a uniform manner. The statistical database contains statistical Z-images and cytoarchitectural population maps in Talairach space. In this study, we use the statistical images to find co-activation patterns for experiments engaging the somatosensory area 3b. Methods: We first made a voxel-wise correlation between all the statistical Z-images and the population map of cytoarchitectural area 3b. The statistical image with the highest correlation had a correlation of 0.20. This image was then used to calculate the voxel-wise correlation with all the other statistical images in the database. Nine statistical images were found to have a higher correlation than 0.10, which was considered fairly high given the small ratio between the size of the activations and the total size of the brain. A sum image was calculated from these images and then normalized in order to regard the noise as ~N(0,1). Finally, we used False Discovery Rate to find the threshold value for a corrected p = 0.01 in the normalized sum image. Results: The threshold level for the normalized sum image was found to be Z ≥ 2.90, which corresponds to an uncorrected p = 0.002 and a corrected p = 0.01. The results show significant activations in the left hemisphere for areas 3b, 4a and 4p (figure 1), and significant bilateral activations for the intraparietal areas ip1 and ip2 (figure 2). No activation was found in area 6. Conclusion: The experiments in the study have in common that they engage area 3b in the left hemisphere. For these experiments, we also found a bilateral co-activation pattern for the areas ip1 and ip2. The chosen method is sensitive to activations that are weak and unsignificant in each individual experiment but reproduced across experiments. There is a clear benefit of such a method compared to meta-analyses of databases with published functional neuroimaging experiments, where only reported findings from each study can be used in the meta-analysis.

Modelling of cortical and thalamic 600Hz activity by means of oscillatory networks

Event Abstract Back to Event Modelling of cortical and thalamic 600Hz activity by means of oscillatory networks Thomas Milde1, 2, Jens Haueisen2, 3, Herbert Witte1, 2 and Lutz Leistritz1, 2* 1 Friedrich Schiller University Jena, Germany 2 Albert-Ludwigs-University, Germany 3 Technical University Ilmenau, Germany The purpose of this study is to investigate information processing in the primary somatosensory system with the help of oscillatory network modelling. Specifically, we consider directed interactions in the oscillatory 600 Hz activity between the thalamus and the cortical Brodmann areas 3b and 1. Electrical stimulation of peripheral somatosensory nerves evokes two types of early brain activity in two distinct frequency ranges that can be detected with electroencephalography (EEG) or magnetoencephalography (MEG). An oscillatory brain activity with a mean frequency at about 650 Hz overlays the initial low-frequency (up to 250 Hz) cortical responses at latencies of 18 to 30 ms after stimulus. Although the origin of the fast oscillatory activity at about 650 Hz is not yet completely clear, this activity will provide a new non-invasive window to the brain, since it is most likely not caused by the excitatory postsynaptic potentials as the common low frequency activity. Our measurements consist of simultaneous 31-channel MEG and 32-channel EEG recordings and individual 3D MRI data. We perform source localization by means of a multi-dipole model. The dipole activation time courses are then modelled by three coupled oscillators, described by linear second-order ordinary delay differential equations (DDEs) with several parameters. The three nodes of the network symbolize the thalamus and the cortical Brodmann areas 3b and 1. The resulting network model may be used to analyze directed information transfer within the somatosensory system. The parameters of the DDE system are successfully fitted to the data of 12 volunteers by an evolutionary optimization method. The pre-stimulus state of the network is defined by zero, which is a fixed point of the DDE. To activate the oscillatory network, an individual input function is used, based on measurements of the propagated stimulation signal measured at the biceps. In accordance with physiological assumptions, the system returns to the pre-stimulus state not later than 35 ms after the stimulus. A significant feedback from the cortex to the thalamus could be detected by comparing the network modelling with and without feedback connections. Our finding in humans is supported by earlier animal studies. We conclude that this type of rhythmic brain activity can be modelled by oscillatory networks in order to disentangle feed forward and feedback information transfer. Conference: Bernstein Symposium 2008, Munich, Germany, 8 Oct - 10 Oct, 2008. Presentation Type: Oral Presentation Topic: All Abstracts Citation: Milde T, Haueisen J, Witte H and Leistritz L (2008). Modelling of cortical and thalamic 600Hz activity by means of oscillatory networks. Front. Comput. Neurosci. Conference Abstract: Bernstein Symposium 2008. doi: 10.3389/conf.neuro.10.2008.01.087 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 17 Nov 2008; Published Online: 17 Nov 2008. * Correspondence: Lutz Leistritz, Friedrich Schiller University Jena, Jena, Germany, Lutz.Leistritz@mti.uni-jena.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Thomas Milde Jens Haueisen Herbert Witte Lutz Leistritz Google Thomas Milde Jens Haueisen Herbert Witte Lutz Leistritz Google Scholar Thomas Milde Jens Haueisen Herbert Witte Lutz Leistritz PubMed Thomas Milde Jens Haueisen Herbert Witte Lutz Leistritz Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Auditory-motor and cognitive aspects in area 8B of macaque monkey’s frontal cortex: a premotor ear–eye field (PEEF)

In previous reports, we showed the involvement of area 8B neurons in both spontaneous ear and eye movement and in auditory information processing. Audition-related cells responded to complex environmental stimuli, but not to pure tones, and their activity changed during visual fixation as a possible inhibitory expression of the engagement of attention. We observed auditory, auditory-motor and motor cells for both eye and ear movements. This finding suggests that area 8B may be involved in the integration of auditory input with ear and eye motor output. In this paper, we extended these previous studies by examining area 8B activity in relation to auditive orienting behaviour, as well as the ocular orientation (i.e., visual fixation) studied previously. Visual fixation led to inhibition of activity in auditory and auditory-motor cells, which suggests that attention may be involved in both, maintaining the eye position and reducing the response of these cell types. Accordingly, during a given task or natural behaviour, spatial attention seems to affect more than one sensorimotor channel simultaneously. These data add to our understanding of how the neural network, through a two-channel attentive process, accomplishes to switch between two effectors, namely eyes and ears. Considering the functional, anatomical and cytoarchitectonic differences among the frontal eye field (FEF), the supplementary eye field (SEF) and area 8B, we propose to consider area 8B as a separate premotor ear-eye field (PEEF).

Organization of anterior cingulate and frontal cortical projections to the retrosplenial cortex in the rat

The retrosplenial cortex (areas 29a-d), which plays an important role in spatial memory and navigation, is known to provide massive projections to frontal association and motor cortices, which are also essential for spatial behavior. The reciprocal projections originating from these frontal cortices to areas 29a-d, however, have been analyzed to only a limited extent. Here, we report an analysis of the anatomical organization of projections from anterior cingulate area 24 and motor and prefrontal cortices to areas 29a-d in the rat, using the axonal transport of cholera toxin B subunit and biotinylated dextran amine. Area 29a receives projections from rostral area 24a, area 24b, the ventral orbital area, and the caudal secondary motor area. Rostral area 29b receives projections from caudal area 24a, whereas caudal area 29b receives projections from rostral area 24a. Area 29b also receives projections from area 24b and the ventral orbital area. Areas 29c and 29d receive projections from areas 24a and 24b and the secondary motor area in a topographic manner such that the rostrocaudal axis of areas 29c and 29d corresponds to the caudorostral axis of areas 24a and 24b and the secondary motor area. Rostral areas 29c and 29d also receive projections from the caudal primary motor area, and area 29d receives projections from the ventral, lateral, and medial orbital areas. These differential frontal cortical projections to each area of the retrosplenial cortex suggest that each area may contribute to different aspects of retrosplenial cortical function such as spatial memory and behavior.

Neural correlates of tactile detection: a combined magnetoencephalography and biophysically based computational modeling study.

Previous reports conflict as to the role of primary somatosensory neocortex (SI) in tactile detection. We addressed this question in normal human subjects using whole-head magnetoencephalography (MEG) recording. We found that the evoked signal (0-175 ms) showed a prominent equivalent current dipole that localized to the anterior bank of the postcentral gyrus, area 3b of SI. The magnitude and timing of peaks in the SI waveform were stimulus amplitude dependent and predicted perception beginning at approximately 70 ms after stimulus. To make a direct and principled connection between the SI waveform and underlying neural dynamics, we developed a biophysically realistic computational SI model that contained excitatory and inhibitory neurons in supragranular and infragranular layers. The SI evoked response was successfully reproduced from the intracellular currents in pyramidal neurons driven by a sequence of lamina-specific excitatory input, consisting of output from the granular layer (approximately 25 ms), exogenous input to the supragranular layers (approximately 70 ms), and a second wave of granular output (approximately 135 ms). The model also predicted that SI correlates of perception reflect stronger and shorter-latency supragranular and late granular drive during perceived trials. These findings strongly support the view that signatures of tactile detection are present in human SI and are mediated by local neural dynamics induced by lamina-specific synaptic drive. Furthermore, our model provides a biophysically realistic solution to the MEG signal and can predict the electrophysiological correlates of human perception.

Ascending inputs to, and internal organization of, cortical motor areas.

Modern anatomical studies show that, contrary to the long-held dogma, there appears to be essentially no convergence of lemniscal, cerebellar, pallidal, or substantial nigral afferents in the thalamus. Each afferent stream defines its own thalamic territory and, through the projection of these thalamic territories to separate cortical territories, the independence of the projections of subcortical motor nuclei upon the cortex is preserved. Only the spinothalamic system appears to gain access to both sensory and motor cortex. A further principle of organization in the sensorimotor thalamus is the presence of individual anatomically and physiologically defined channels, composed of separate afferent inputs and groups of neurons relaying to the cortex. In the somatic sensory relay nuclei the dissociation of cutaneous, deep slowly and rapidly adapting channels is clear-cut in the thalamus and at the input level of the cortex. In the motor system, inputs from each of the deep cerebellar nuclei appear to be dissociated from one another in the thalamus and these in turn from the vestibular and spinothalamic systems. Just as pallidal, nigral and cerebellar pathways are in position to control separate premotor and motor areas of the cortex, so separate channels leading through VLp appear to be in a position to control separate functional units in area 4. Within the cortex itself the absence of corticocortical connections passing from areas 3a and 3b to area 4 appears to indicate that information flow out of these areas is back to areas 1 and 2 for further processing before transmission to area 4 with all the consequences that entails for sensory convergence. Presumably, this route is sufficiently rapid for sensory inputs to reach area 4 at short latency. Although many data are beginning to accrue on the intrinsic structure and connectivity of the sensorimotor cortex, we are still distant from a complete wiring diagram. Circuitry involving thalamic afferents is becoming known slowly and the nature of the cells that are present and their transmitter characteristics are becoming evident from morphological and immunocytochemical studies, along with information on the patterns of axonal ramification of specific cell types, especially of GABAergic cells and of excitatory corticocortical cells.

Relationship between the corticostriatal terminals from areas 9 and 46, and those from area 8A, dorsal and rostral premotor cortex and area 24c: an anatomical substrate for cognition to action

Our previous data indicate that there are specific features of the corticostriatal pathways from the prefrontal cortex. First, corticostriatal pathways are composed of focal, circumscribed projections and of diffuse, widespread projections. Second, there is some convergence between terminal fields from different functional regions of the prefrontal cortex. Third, anterior cingulate projections from area 24b occupy a large region of the rostral striatum. The goal of this study was to determine whether these features are also common to the corticostriatal projections from area 8A (including the frontal eye field; FEF), the supplementary eye field (SEF), dorsal and rostral premotor cortex (PMdr) and area 24c. Using a new approach of three-dimensional reconstruction of the corticostriatal pathways, along with dual cortical tracer injections, we mapped the corticostriatal terminal fields from areas 9 and 46, 8A-FEF, SEF, PMdr and 24b and c. In addition, we placed injections of retrogradely transported tracers into key striatal regions. The results demonstrated that: (i) a diffuse projection system is a common feature of the corticostriatal projections from different frontal regions; (ii) key striatal regions receive convergent projections from areas 9 and 46 and from areas 8A-FEF, SEF, PMdr and 24c, suggesting a potential pivotal role of these striatal regions in integrating cortical information; (iii) projections from area 24c, like those from area 24b, terminate widely throughout the striatum, interfacing with terminals from several frontal areas. These features of the corticostriatal frontal pathways suggest a potential integrative striatal network for learning.

Interference of tactile and pain stimuli on thalamocortical signal processing in humans revealed by median nerve SEPs

Objective We investigated the interference of tactile and painful stimuli on human early somatosensory evoked potentials (SEPs) including high frequency oscillations (HFOs) to further study thalamocortical processing of somatosensory information. Methods Multi-channel median nerve SEPs were recorded during (1) no interference, (2) sensory interference by tactile stimulation to digits 2 and 3, and (3) application of pain to the same digits. Spatio-temporal source analysis separated brain stem (S1), thalamic (S2) and two cortical sources (S3, S4), which were evaluated for the low (20–450 Hz) and high (450–750 Hz) frequency portion of the signal. Results Low frequency SEPs showed a decrease of activity at cortical source S3 during both conditions, while thalamic source S2 was significantly increased during pain interference. HFOs showed an increase of cortical source S3 and in trend of thalamic source S2 and cortical source S4 during both kinds of interference. Conclusions Although the painful stimulus might not be specific for the nociceptive afferents, the present data affirm that at this early stage of sensory information processing within the primary sensory cortex (area 3b, area 1) pain is handled similar to sensory interference. Significance HFOs might represent an intrinsic “somatosensory alerting” system which reacts to both interference stimuli in a similar way, therefore indicating an interference without a qualitative evaluation.

High-Resolution Maps of Real and Illusory Tactile Activation in Primary Somatosensory Cortex in Individual Monkeys with Functional Magnetic Resonance Imaging and Optical Imaging

Although blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) has been widely used to explore human brain function, questions remain regarding the ultimate spatial resolution of positive BOLD fMRI, and indeed the extent to which functional maps revealed by positive BOLD correlate spatially with maps obtained with other high-spatial-resolution mapping techniques commonly used in animals, such as optical imaging of intrinsic signal (OIS) and single-unit electrophysiology. Here, we demonstrate that the positive BOLD signal at 9.4T can reveal the fine topography of individual fingerpads in single-condition activation maps in nonhuman primates. These digit maps are similar to maps obtained from the same animal using intrinsic optical imaging. Furthermore, BOLD fMRI reliably resolved submillimeter spatial shifts in activation in area 3b previously identified with OIS (Chen et al., 2003) as neural correlates of the "funneling illusion." These data demonstrate that at high field, high-spatial-resolution topographic maps can be achieved using the positive BOLD signal, weakening previous notions regarding the spatial specificity of the positive BOLD signal.

Cognitive MR spectroscopy of anterior cingulate cortex in ADHD: Elevated choline signal correlates with slowed hit reaction times

The anterior cingulate cortex (ACC) plays a major role in modulating executive control of attention. Here, 15 medication-naı¨ve patients with attention deficit/hyperactivity disorder (ADHD) and 10 carefully matched healthy controls were studied with 2D 1H-magnetic resonance spectroscopic imaging (MRSI) of the ACC [Brodmann areas 24b′-c′ and 32′]. Attentional skills were assessed using the identical pairs version of the continuous performance task (CPT-IP). Analysis of regional brain spectra revealed a significantly increased signal of choline-containing compounds (Ch) in the ACC of ADHD patients ( p < 0.05). Across and within groups, the Ch signal showed high correlations with slowed hit reaction times on the CPT-IP. No group differences in N-acetyl-aspartate (NAA) and creatine (tCr) were detectable. The combination of performance deficits and elevated Ch levels in the ACC supports the hypothesis that subtle structural abnormalities underlie the functional alterations in ACC activation previously observed in ADHD patients.

Dependence of BOLD signal change on tactile stimulus intensity in SI of primates

Recently, we have demonstrated that the fine-digit topography (millimeter sized) previously identified in the primary somatosensory cortex (SI), using electrophysiology and intrinsic signal optical imaging, can also be mapped with submillimeter resolution using blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging at high field. In the present study, we have examined the dependence of BOLD signal response on stimulus intensity in two subregions of SI, Areas 3b and 1. In a region(s)-of-interest (ROI) analysis of Area 3b, BOLD signal amplitude increased linearly with increasing amplitude of an 8-Hz vibrotactile stimulus, and BOLD signal was sustained throughout the stimulation period. In contrast, in Area 1, a significant BOLD signal response was only observed with more intense stimuli, and ROI analysis of the dependence of BOLD response showed no significant dependence on stimulus intensity. In addition, activation was not sustained throughout the period of stimulation. Differing responses of Areas 3b and 1 suggest potentially divergent roles for subregions of SI cortices in vibrotactile intensity encoding. Moreover, this study underscores the importance of imaging at small spatial scales. In this case, such high-resolution imaging allows differentiation between area-specific roles in intensity encoding and identifies anatomic targets for detailed electrophysiological studies of somatosensory neuronal populations with different coding properties. These experiments illustrate the value of nonhuman primates for characterizing the dependence of the BOLD signal response on stimulus parameters and on underlying neural response properties.

LTP‐like changes induced by paired associative stimulation of the primary somatosensory cortex in humans: source analysis and associated changes in behaviour

Paired associative stimulation (PAS), which combines repetitive peripheral nerve stimulation with transcranial magnetic stimulation (TMS), may induce neuroplastic changes in somatosensory cortex (S1), possibly by long-term potentiation-like mechanisms. We used multichannel median nerve somatosensory evoked potential (MN-SSEP) recordings and two-point tactile discrimination testing to examine the location and behavioural significance of these changes. When TMS was applied to S1 near-synchronously to an afferent signal containing mechanoreceptive information, MN-SSEP changes (significant at 21-31 ms) could be explained by a change in a tangential source located in Brodmann area 3b, with their timing and polarity suggesting modification of upper cortical layers. PAS-induced MN-SSEP changes between 28 and 32 ms were linearly correlated with changes in tactile discrimination. Conversely, when the near-synchronous afferent signal contained predominantly proprioceptive information, PAS-induced MN-SSEP changes (20-29 ms) were shifted medially, and tactile performance remained stable. With near-synchronous mechanoreceptive stimulation subtle differences in the timing of the two interacting signals tended to influence the direction of tactile performance changes. PAS performed with TMS delivered asynchronously to the afferent pulse did not change MN-SSEPs. Hebbian interaction of mechanoreceptive afferent signals with TMS-evoked activity may modify synaptic efficacy in superficial cortical layers of Brodmann area 3b and is associated with timing-dependent and qualitatively congruent behavioural changes.

Identifying mutual information transfer in the brain with differential-algebraic modeling: Evidence for fast oscillatory coupling between cortical somatosensory areas 3b and 1

Understanding information transfer in the brain is a major challenge in today’s neurosciences. Commonly, information transfer between brain areas is analyzed with the help of correlation measures for electrophysiological data. However, such approaches cannot distinguish between mutual coupling and other mechanisms of creating correlations between responses, such as common input from other sources. Functional coupling is mandatory for information transfer. Here we propose to analyze coupling between active brain areas with the help of models described by a system of differential-algebraic equations. Comparing models with various degrees of coupling, we show that mutual information transfer can be distinguished from one-way information transfer for activated cortical areas estimated by source localization techniques. We exemplify the technique with fast oscillatory activity found in both cortical areas 3b and 1 after peripheral nerve stimulation.

Exposure to Ethanol during Gastrulation Alters Somatosensory-Motor Cortices and the Underlying White Matter in the Macaque

The present study tests the hypothesis that a critical window for cortical development coincides with the period of neural stem cell proliferation (during the first 6 weeks of gestation), specifically, gastrulation (on embryonic day [E] 19 and E20). Pregnant female macaques were exposed to ethanol 1 day/week for 6 or 24 weeks such that it included E19 or E20 or a time before or after the time of gastrulation. Total forebrain size was increased in macaques exposed to ethanol on E19 or E20. Thus, various features of the gray and white matter of the paracentral lobule of adolescent offspring were examined. Ethanol exposure affected the gray matter, for example, the 1.63 billion neurons in somatosensory cortex of controls (areas 3a and 3b) was 32% lower in ethanol-exposed monkeys, but neither duration nor timing of the episodic exposure had a differential effect. In contrast, the timing of the exposure during the third week critically affected the amount of white matter (the mass of myelopil, but not cell number). Therefore, fetal exposure to ethanol unveils a normal programming mechanism wherein neural stem cells appear to be a target and a critical window for forebrain development concurs with gastrulation.

Tactile Hyperacuity Thresholds Correlate with Finger Maps in Primary Somatosensory Cortex (S1)

Behavioral tactile discrimination thresholds were compared with functional magnetic resonance imaging measurements of cortical finger representations within primary somatosensory cortex (S1) for 10 human subjects to determine whether cortical magnification in S1 could account for the variation in tactile hyperacuity thresholds of the fingers. Across 10 subjects, the increase in tactile thresholds from the index finger to the little finger correlated with the decrease in cortical representation across fingers in S1. Additionally, representations of the fingers within S1, in Brodmann areas 3b and 1, were also correlated with the thresholds. These results suggest that tactile hyperacuity is largely determined by the cortical representation of the fingers in S1.

Organization of sensory neocortex in prairie voles (Microtus ochrogaster)

In the current investigation, the functional organization of visual, auditory, and somatosensory cortex was examined in prairie voles (Microtus ochrogaster) by using electrophysiological recording techniques. Functional boundaries of cortical fields were directly related to myeloarchitectonic boundaries. Our results demonstrated that most of the neocortex is occupied by the visual, auditory, and somatosensory areas. Specifically, a small area 17, or primary visual area (V1), was located on the caudomedial pole of the neocortex; a large auditory cortex (AC), which contains the primary auditory area (A1) and other auditory fields, encompassed almost the entire temporal pole; and a large area 3b, or primary somatosensory area (S1), contained a complete representation of the contralateral body surface. Furthermore, these areas were coextensive with distinct myeloarchitectonic appearances. We also observed that the AC appeared to be disproportionately large in the prairie vole compared with other rodents. In addition, we found that both primary and nonprimary areas contained neurons that responded to auditory stimulation. Finally, we observed within S1 a disproportionate amount of cortex that was devoted to representing the perioral hairs and the snout and also that neurons within this representation had very small receptive fields. We discuss the expanded auditory domain and the enlarged representation of perioral hairs as they relate to the specialized life style of the prairie vole.

Spatiotemporal integration of tactile information in human somatosensory cortex

BackgroundOur goal was to examine the spatiotemporal integration of tactile information in the hand representation of human primary somatosensory cortex (anterior parietal somatosensory areas 3b and 1), secondary somatosensory cortex (S2), and the parietal ventral area (PV), using high-resolution whole-head magnetoencephalography (MEG). To examine representational overlap and adaptation in bilateral somatosensory cortices, we used an oddball paradigm to characterize the representation of the index finger (D2; deviant stimulus) as a function of the location of the standard stimulus in both right- and left-handed subjects.ResultsWe found that responses to deviant stimuli presented in the context of standard stimuli with an interstimulus interval (ISI) of 0.33s were significantly and bilaterally attenuated compared to deviant stimulation alone in S2/PV, but not in anterior parietal cortex. This attenuation was dependent upon the distance between the deviant and standard stimuli: greater attenuation was found when the standard was immediately adjacent to the deviant (D3 and D2 respectively), with attenuation decreasing for non-adjacent fingers (D4 and opposite D2). We also found that cutaneous mechanical stimulation consistently elicited not only a strong early contralateral cortical response but also a weak ipsilateral response in anterior parietal cortex. This ipsilateral response appeared an average of 10.7 ± 6.1 ms later than the early contralateral response. In addition, no hemispheric differences either in response amplitude, response latencies or oddball responses were found, independent of handedness.ConclusionOur findings are consistent with the large receptive fields and long neuronal recovery cycles that have been described in S2/PV, and suggest that this expression of spatiotemporal integration underlies the complex functions associated with this region. The early ipsilateral response suggests that anterior parietal fields also receive tactile input from the ipsilateral hand. The lack of a hemispheric difference in responses to digit stimulation supports a lack of any functional asymmetry in human somatosensory cortex.

Characterization of the effect of associative cortical and peripheral nerve stimulation on the somatosensory evoked potentials and tactile discrimination performance in human subjects

Repetitive median nerve stimulation combined with transcranial magnetic stimulation (TMS) over the contralateral postcentral region (paired associative stimulation, PAS) may induce changes in the amplitude of the P25 component of median nerve somatosensory evoked potentials (MN-SSEP). Here we used 64-channel electroencephalography (EEG) to reveal the early cortical MN-SSEP source(s) that is modified by PAS. In addition, spatial two-point discrimination was tested one day before (day1), immediately after (day2) and one day after (day3) PAS-intervention to assess possible changes of tactile sensitivity corresponding to somatosensory representations inside or outside of the cortical PAS-target, respectively. Eleven healthy volunteers participated in five experiments. MN-SSEPs (1800 trials, ˜3 Hz, 300% perceptual threshold) were recorded before and after PAS intervention. During the intervention the magnetic pulse (180 repetitions at 0.1 Hz, 150% resting motor threshold) was delivered over S1 at one of the following times relative to the subject’s N20 peak: −20, −2.5, 0 and 100 ms (PASN20 − 20, PASN20 − 2.5, PASN20 + 0, PASN20 + 100 ms, respectively). As a control, the TMS pulse was delivered at half time between two median nerve stimulations (PAS+5 s). Following PASN20 − 2.5 and PASN20 + 100 ms, a nonparametric permutation test across all subjects revealed an EEG amplitude increase between 21 and 31 ms. Source analysis showed that the effect of PASN20 − 2.5 ms could be accounted for by an amplitude increase of a tangential source localized at S1. The effect of PASN20 + 100 ms differed in its scalp topography from that of PASN20 − 2.5 ms and may be attributed to a different source at S1. In addition, PAS induced differential effects on tactile performance. Following PASN20 − 20 ms, performance in D2, but not in D5, improved significantly. In contrast, following PASN20 − 2.5 ms, there was a tendency for deterioration in tactile performance of the index finger which was correlated with MN-SSEP changes between 28 and 32 ms (R2 = 0.8). These results lend support to the notion that PASN20 − 2.5 modifies synapses located in superficial cortical layers in Brodmann area 3b and thereby may induce spatially specific differential behavioral changes in tactile performance.

Cortical and thalamic connections of the representations of the teeth and tongue in somatosensory cortex of new world monkeys

Connections of representations of the teeth and tongue in primary somatosensory cortex (area 3b) and adjoining cortex were revealed in owl, squirrel, and marmoset monkeys with injections of fluorescent tracers. Injection sites were identified by microelectrode recordings from neurons responsive to touch on the teeth or tongue. Patterns of cortical label were related to myeloarchitecture in sections cut parallel to the surface of flattened cortex, and to coronal sections of the thalamus processed for cytochrome oxidase (CO). Cortical sections revealed a caudorostral series of myelin dense ovals (O1-O4) in area 3b that represent the periodontal receptors of the contralateral teeth, the contralateral tongue, the ipsilateral teeth, and the ipsilateral tongue. The ventroposterior medial subnucleus, VPM, and the ventroposterior medial parvicellular nucleus for taste, VPMpc, were identified in the thalamic sections. Injections placed in the O1 oval representing teeth labeled neurons in VPM, while injections in O2 representing the tongue labeled neurons in both VPMpc and VPM. These injections also labeled adjacent part of areas 3a and 1, and locations in the lateral sulcus and frontal lobe. Callosally, connections of the ovals were most dense with corresponding ovals. Injections in the area 1 representation of the tongue labeled neurons in VPMpc and VPM, and ipsilateral area 3b ovals, area 3a, opercular cortex, and cortex in the lateral sulcus. Contralaterally, labeled neurons were mostly in area 1. The results implicate portions of areas 3b, 3a, and 1 in the processing of tactile information from the teeth and tongue, and possibly taste information from the tongue.