The normal development of the somatosensory system requires intact sensory inputs from the periph... more The normal development of the somatosensory system requires intact sensory inputs from the periphery during a critical window of time early in development. Here we determined how the removal of only part of the ascending spinal inputs early in development affects the anatomical and neurophysiological development of the somatosensory system. We performed spinal overhemisections in rat pups at C3/C4 levels
To understand how information is coded in the primary somatosensory cortex (S1) we need to deciph... more To understand how information is coded in the primary somatosensory cortex (S1) we need to decipher the relationship between neural activity and tactile stimuli. Such a relationship can be formally measured by mutual information. The present study was designed to determine how S1 neuronal populations code for the multidimensional kinetic features (i.e. random, time-varying patterns of force) of complex tactile stimuli, applied at different locations of the rat forepaw. More precisely, the stimulus localization and feature extraction were analyzed as two independent processes, using both rate coding and temporal coding strategies. To model the process of stimulus kinetic feature extraction, multidimensional stimuli were projected onto lower dimensional subspace and then clustered according to their similarity. Different combinations of stimuli clustering were applied to differentiate each stimulus identification process. Information analyses show that both processes are synergistic, this synergy is enhanced within the temporal coding framework. The stimulus localization process is faster than the stimulus feature extraction process. The latter provides more information quantity with rate coding strategy, whereas the localization process maximizes the mutual information within the temporal coding framework. Therefore, combining mutual information analysis with robust clustering of complex stimuli provides a framework to study neural coding mechanisms related to complex stimuli discrimination.
We investigated the effects of sensory deprivation on the forepaw representation in the primary s... more We investigated the effects of sensory deprivation on the forepaw representation in the primary somatosensory cortex (SI) in the adult rat. Cortical maps were constructed from high-resolution multiunit recordings of the response of layer IV neurons to somatosensory stimuli. The main features of the forepaw representation were described in terms of areal extent and topography of the cortical map, and sensory submodality, size, and location of the receptive field (RF) of small clusters of the cortical neurons. After being weaned, two groups of Long-Evans rats were housed in a standard (SE) or impoverished (IE) environment for 65-115 days. A third group of SE rats was subjected to severe sensorimotor restriction (SR) of one forepaw for 7 days or 14 days, by using a one-sleeved cast. A concomitant effect of unilateral forelimb immobilization was a forced use of the nonrestricted forelimb in postural balance. The maps of both forepaws were derived 24 h after the cast was removed and the animal was allowed normal limb use. In a fourth group, SE rats experienced a 7-day immobilization followed by symmetrical limb use for 7 days before we mapped the hemisphere contralateral to the casted limb. For the SE and IE rats, the total areal extent of the cutaneous forepaw representation was similar, but IE rats exhibited a significant expansion of cortical islets serving high-threshold, presumably noncutaneous inputs, which were included in the cutaneous maps. In addition, SI neurons of IE rats had greatly enlarged glabrous, but not hairy, skin RFs. For the SR rats, the areal extent of the cutaneous map of the casted forepaw decreased by about 50%, after both 7- and 14-day forelimb immobilization. Large cortical sectors presumed to be formerly activated by cutaneous inputs were driven by high-threshold inputs that disrupted the somatotopic representation of the forepaw skin surfaces. These "emergent" representational sectors were topographically organized. By contrast, the areal extent and topography of the non-casted forepaw representation did not differ from those of SE rats. The size of glabrous RFs on the casted forepaw was similar to that of SE rats. On the contrary, glabrous RFs on the noncasted forepaw of SR rats were larger than those on their casted forepaw. The size of hairy RFs was not altered by the forelimb restriction. Interestingly, alteration of the somatotopic features of the casted forepaw map persisted after 7 days of symmetric use of the forelimbs. The present study demonstrates that continuous sensory experience is needed for the organizational features of SI maps to be maintained.
The organization of anterior and lateral somatosensory cortex was investigated in titi monkeys (C... more The organization of anterior and lateral somatosensory cortex was investigated in titi monkeys (Callicebus moloch). Multiunit microelectrode recordings were used to identify multiple representations of the body, and anatomical tracer injections were used to reveal connections. (1) Representations of the face were identified in areas 3a, 3b, 1, S2, and the parietal ventral area (PV). In area 3b, the face was represented from chin/lower lip to upper lip and neck/upper face in a rostrocaudal sequence. The representation of the face in area 1 mirrored that of area 3b. Another face representation was located in area 3a. Adjoining face representations in S2 and PV exhibited mirror-image patterns to those of areas 3b and 1. (2) Two representations of the body, the rostral and caudal ventral somatosensory areas (VSr and VSc), were found in the dorsal part of the insula. VSc was roughly a reversal image of the S2 body representation, and VSr was roughly a reversal of PV. (3) Neurons in the insula next to VSr and VSc responded to auditory stimuli or to both auditory and somatosensory stimuli. (4) Injections of tracers within the hand representations in areas 3b, 1, and S2 revealed reciprocal connections between these three areas. Injections in areas 3b and 1 labeled the ventroposterior nucleus, whereas injections in S2 labeled the inferior ventroposterior nucleus. The present study demonstrates features of somatosensory cortex of other monkeys in titi monkeys, while revealing additional features that likely apply to other primates.
The normal development of the somatosensory system requires intact sensory inputs from the periph... more The normal development of the somatosensory system requires intact sensory inputs from the periphery during a critical window of time early in development. Here we determined how the removal of only part of the ascending spinal inputs early in development affects the anatomical and neurophysiological development of the somatosensory system. We performed spinal overhemisections in rat pups at C3/C4 levels
To understand how information is coded in the primary somatosensory cortex (S1) we need to deciph... more To understand how information is coded in the primary somatosensory cortex (S1) we need to decipher the relationship between neural activity and tactile stimuli. Such a relationship can be formally measured by mutual information. The present study was designed to determine how S1 neuronal populations code for the multidimensional kinetic features (i.e. random, time-varying patterns of force) of complex tactile stimuli, applied at different locations of the rat forepaw. More precisely, the stimulus localization and feature extraction were analyzed as two independent processes, using both rate coding and temporal coding strategies. To model the process of stimulus kinetic feature extraction, multidimensional stimuli were projected onto lower dimensional subspace and then clustered according to their similarity. Different combinations of stimuli clustering were applied to differentiate each stimulus identification process. Information analyses show that both processes are synergistic, this synergy is enhanced within the temporal coding framework. The stimulus localization process is faster than the stimulus feature extraction process. The latter provides more information quantity with rate coding strategy, whereas the localization process maximizes the mutual information within the temporal coding framework. Therefore, combining mutual information analysis with robust clustering of complex stimuli provides a framework to study neural coding mechanisms related to complex stimuli discrimination.
We investigated the effects of sensory deprivation on the forepaw representation in the primary s... more We investigated the effects of sensory deprivation on the forepaw representation in the primary somatosensory cortex (SI) in the adult rat. Cortical maps were constructed from high-resolution multiunit recordings of the response of layer IV neurons to somatosensory stimuli. The main features of the forepaw representation were described in terms of areal extent and topography of the cortical map, and sensory submodality, size, and location of the receptive field (RF) of small clusters of the cortical neurons. After being weaned, two groups of Long-Evans rats were housed in a standard (SE) or impoverished (IE) environment for 65-115 days. A third group of SE rats was subjected to severe sensorimotor restriction (SR) of one forepaw for 7 days or 14 days, by using a one-sleeved cast. A concomitant effect of unilateral forelimb immobilization was a forced use of the nonrestricted forelimb in postural balance. The maps of both forepaws were derived 24 h after the cast was removed and the animal was allowed normal limb use. In a fourth group, SE rats experienced a 7-day immobilization followed by symmetrical limb use for 7 days before we mapped the hemisphere contralateral to the casted limb. For the SE and IE rats, the total areal extent of the cutaneous forepaw representation was similar, but IE rats exhibited a significant expansion of cortical islets serving high-threshold, presumably noncutaneous inputs, which were included in the cutaneous maps. In addition, SI neurons of IE rats had greatly enlarged glabrous, but not hairy, skin RFs. For the SR rats, the areal extent of the cutaneous map of the casted forepaw decreased by about 50%, after both 7- and 14-day forelimb immobilization. Large cortical sectors presumed to be formerly activated by cutaneous inputs were driven by high-threshold inputs that disrupted the somatotopic representation of the forepaw skin surfaces. These "emergent" representational sectors were topographically organized. By contrast, the areal extent and topography of the non-casted forepaw representation did not differ from those of SE rats. The size of glabrous RFs on the casted forepaw was similar to that of SE rats. On the contrary, glabrous RFs on the noncasted forepaw of SR rats were larger than those on their casted forepaw. The size of hairy RFs was not altered by the forelimb restriction. Interestingly, alteration of the somatotopic features of the casted forepaw map persisted after 7 days of symmetric use of the forelimbs. The present study demonstrates that continuous sensory experience is needed for the organizational features of SI maps to be maintained.
The organization of anterior and lateral somatosensory cortex was investigated in titi monkeys (C... more The organization of anterior and lateral somatosensory cortex was investigated in titi monkeys (Callicebus moloch). Multiunit microelectrode recordings were used to identify multiple representations of the body, and anatomical tracer injections were used to reveal connections. (1) Representations of the face were identified in areas 3a, 3b, 1, S2, and the parietal ventral area (PV). In area 3b, the face was represented from chin/lower lip to upper lip and neck/upper face in a rostrocaudal sequence. The representation of the face in area 1 mirrored that of area 3b. Another face representation was located in area 3a. Adjoining face representations in S2 and PV exhibited mirror-image patterns to those of areas 3b and 1. (2) Two representations of the body, the rostral and caudal ventral somatosensory areas (VSr and VSc), were found in the dorsal part of the insula. VSc was roughly a reversal image of the S2 body representation, and VSr was roughly a reversal of PV. (3) Neurons in the insula next to VSr and VSc responded to auditory stimuli or to both auditory and somatosensory stimuli. (4) Injections of tracers within the hand representations in areas 3b, 1, and S2 revealed reciprocal connections between these three areas. Injections in areas 3b and 1 labeled the ventroposterior nucleus, whereas injections in S2 labeled the inferior ventroposterior nucleus. The present study demonstrates features of somatosensory cortex of other monkeys in titi monkeys, while revealing additional features that likely apply to other primates.
Uploads
Papers by Jacques-olivier Coq