Biomedical subjects

Michael S Remple

Publications and source records attributed to Michael S Remple.

8 recordsLinked to original sources

PubMed2007

The organization of frontoparietal cortex in the tree shrew (Tupaia belangeri): II. Connectional evidence for a frontal-posterior parietal network.

Tree shrews are small squirrel-like mammals that are the closest living relative to primates available for detailed neurobiological study. In a recent study (Remple et al. [2006] J. Comp. Neurol. 497:133-154), we provided anatomical and electrophysiological evidence that the frontoparietal cortex of tree shrews has two motor fields (M1 and M2) and five somatosensory fields (3a, 3b, S2, somatosensory caudal area [SC], and parietal ventral area [PV]). In the present study, we injected anatomical tracers into M1, M2, 3a, 3b, SC, and posterior parietal cortex to establish the ipsilateral cortical connections of these areas. The results provide evidence for a number of new cortical areas including medial motor and somatosensory areas (MMA and MSA), three posterior parietal areas (PPd, PPv, and PPc), and an area ventral to temporal inferior cortex (TIV). Ml receives topographic projections from M2, MMA, 3a, and PPv, and nontopographic connections from the temporal anterior and dorsal areas (TA and TD), PPc, TIV, and MSA. The connections of M2 are similar to those of M1, except that M2 receives denser projections from TIV, PPc, and dorsal frontal cortex and sparser input from M1. Areas 3a, 3b, and SC receive dense topographic projections from each other, S2, and PV and sparser connections from PPd and PPv. Area 3a receives additional input from posterior parietal and temporal regions and from M1 and MMA. Overall, the frontoparietal connections of tree shrew cortex are most similar to those of prosimian primates and quite different from those of more distant relatives such as rats.

Animals↗

PubMed2006

Motor training induces experience-specific patterns of plasticity across motor cortex and spinal cord.

The motor cortex and spinal cord possess the remarkable ability to alter structure and function in response to differential motor training. Here we review the evidence that the corticospinal system is not only plastic but that the nature and locus of this plasticity is dictated by the specifics of the motor experience. Skill training induces synaptogenesis, synaptic potentiation, and reorganization of movement representations within motor cortex. Endurance training induces angiogenesis in motor cortex, but it does not alter motor map organization or synapse number. Strength training alters spinal motoneuron excitability and induces synaptogenesis within spinal cord, but it does not alter motor map organization. All three training experiences induce changes in spinal reflexes that are dependent on the specific behavioral demands of the task. These results demonstrate that the acquisition of skilled movement induces a reorganization of neural circuitry within motor cortex that supports the production and refinement of skilled movement sequences. We present data that suggest increases in strength may be mediated by an increased capacity for activation and/or recruitment of spinal motoneurons while the increased metabolic demands associated with endurance training induce cortical angiogenesis. Together these results show the robust pattern of anatomic and physiological plasticity that occurs within the corticospinal system in response to differential motor experience. The consequences of such distributed, experience-specific plasticity for the encoding of motor experience by the motor system are discussed.

Action Potentials↗

PubMed2006

Organization of frontoparietal cortex in the tree shrew (Tupaia belangeri). I. Architecture, microelectrode maps, and corticospinal connections.

Despite extensive investigation of the motor cortex of primates, little is known about the organization of motor cortex in tree shrews, one of their closest living relatives. We investigated the organization of frontoparietal cortex in Belanger's tree shrews (Tupaia belangeri) by using intracortical microstimulation (ICMS), corticospinal tracing, and detailed histological analysis. The results provide evidence for the subdivision of tree shrew frontoparietal cortex into seven distinct areas (five are newly identified), including two motor fields (M1 and M2) and five somatosensory fields (3a, 3b, S2, PV, and SC). The types of movements evoked in M1 and M2 were similar, but M2 required higher currents to elicit movements and had few connections to the cervical spinal cord and distinctive cyto- and immunoarchitecture. The borders between M1 and the anterior somatosensory regions (3a and 3b) were identified primarily from histological analysis, because thresholds were similar between these regions, and differences in corticospinal neuron distribution were subtle. The caudal (SC) and lateral (S2 and PV) somatosensory fields were identified based on differences in architecture and distribution of corticospinal neurons. Myelin-dense modules were identified in lateral cortex, in the expected location of the oral, forelimb, and hindlimb representations of S2, and possibly PV. Evidence for a complex primate-like array of motor fields is lacking in tree shrews, but their motor cortex shares a number of basic features with that of primates, which are not found in more distantly related species, such as rats.

Animals↗

PubMed2006

Organization of somatosensory cortical areas in the naked mole-rat (Heterocephalus glaber).

Multiunit electrophysiology was combined with histological analysis of cortical sections to investigate the organization of somatosensory areas in the naked mole-rat. We provide new details for the organization of primary somatosensory cortex (S1) and identify cortical modules and barrels that correspond to the representations of different body parts. In addition, details of the location and organization of secondary somatosensory cortex (S2) are reported, and evidence for a third somatosensory representation, likely the parietal ventral area (PV), is provided and discussed. S1 contained a complete and systematic representation of the contralateral body surface and oral structures. The orientation of S1 was inverted, with the lower body represented medially and the face and oral structures located rostrolaterally. The S2 representation was found in caudolateral cortex forming a mirror image of S1. The two areas were joined at the representation of the vibrissae and snout, so that the orientation of S2 formed an upright representation of the body in cortex. Receptive fields for S2 were consistently larger than those in S1. Evidence for the presumptive parietal ventral area, lateral to S2, suggests that this area may be an inverted mirror image of S2. By aligning the electrophysiological maps of body representations with cytochrome oxidase-reacted cortical sections we were able to identify modules related to the buccal pad, chin, vibrissae, forelimb, hindlimb, trunk, tongue, lower incisor, and upper incisors. The orofacial modules in lateral cortex resemble similar modules reported to relate to oral structures previously described in the laboratory rat, owl monkey, and squirrel monkey.

Animals↗

PubMed2004

Bilateral effects of spinal overhemisections on the development of the somatosensory system in rats.

Connections of the forepaw regions of somatosensory cortex (S1) were determined in rats reared to maturity after spinal cord overhemisections at cervical level C3 on postnatal day 3. Overhemisections cut all ascending and descending pathways and intervening gray on one side of the spinal cord and the pathways of the dorsal funiculus contralaterally. Bilateral lesions of the dorsal columns reduced the size of the brainstem nuclei by 41%, and the ventroposterior lateral subnucleus (VPL) of the thalamus by 20%. Bilateral lesions also prevented the emergence of the normal cytochrome oxidase barrel pattern in forepaw and hindpaw regions of S1. Injections of wheat germ agglutinin conjugated to horseradish peroxidase were placed in the forepaw region of granular S1 and surrounding dysgranular S1 contralateral to the hemisection. The VPL nucleus was densely labeled, whereas the adjoining ventroposterior medial subnucleus, VPM, representing the head, was unlabeled. Thus, there was no evidence of abnormal connections of VPM to forepaw cortex. Foci of transported label in the ipsilateral hemisphere appeared to be in normal locations and of normal extents, but connections in the opposite hemisphere were broadly and nearly uniformly distributed in sensorimotor cortex in a pattern similar to that in postnatal rats. Rats with incomplete lesions that spared the dorsal column pathway on the left side but not the right demonstrated surprisingly normal distributions of callosal connections in the nondeprived right hemisphere, even though the injected left hemisphere was deprived. Thus, the development of the normal pattern of callosal connections depends on dorsal column input and not on normal interhemsipheric interactions.

Afferent Pathways↗

PubMed2003

Organization of somatosensory cortex in the laboratory rat (Rattus norvegicus): Evidence for two lateral areas joined at the representation of the teeth.

Lateral somatosensory areas have not been explored in detail in rats, and theories on the organization of this region are based largely on anatomical tracing experiments. We investigated the topography of this region by using microelectrode recordings, which were related to flattened cortical sections processed for cytochrome oxidase (CO). Two lateral somatosensory areas were identified, each containing a complete representation of the body. A larger, more medial representation formed a mirror image of S1 along the rostrocaudal axis of the head region corresponding to the previously identified secondary somatosensory area (S2). A smaller, more lateral representation formed a mirror image of S2 along the rostrocaudal axis of the forelimb and hindlimb regions and likely corresponds to the parietal ventral area (PV) identified in other mammals. We also investigated the representation of the dentition and identified regions of cortex responsive to tooth stimulation. The lower incisor representation was rostral to the lower lip region of S1, and the upper incisor representation was lateral to the buccal pad region of S1. The upper and lower incisors flanked the tongue representation. An additional large region of far lateral cortex responded to both incisors. Finally, five CO-dense modules were consistently identified rostral and lateral to the S1 face representation, which we refer to as OM1, OM2, OM3, FM, and HM. These modules closely correspond to the physiologically identified areas representing the lower incisor (OM1) and tongue (OM2) regions of S1 and the mixed tooth (OM3), forelimb (FM1), and hindlimb (HM) representations of S2 and PV.

Animals↗

PubMed2002

Somatosensory cortex dominated by the representation of teeth in the naked mole-rat brain.

We investigated naked mole-rat somatosensory cortex to determine how brain areas are modified in mammals with unusual and extreme sensory specializations. Naked mole-rats (Heterocephalus glaber) have numerous anatomical specializations for a subterranean existence, including rows of sensory hairs along the body and tail, reduced eyes, and ears sensitive to low frequencies. However, chief among their adaptations are behaviorally important, enlarged incisors permanently exterior to the oral cavity that are used for digging, object manipulation, social interactions, and feeding. Here we report an extraordinary brain organization where nearly one-third (31%) of primary somatosensory cortex is devoted to the representations of the upper and lower incisors. In addition, somatosensory cortex is greatly enlarged (as a proportion of total neocortical area) compared with closely related laboratory rats. Finally, somatosensory cortex in naked mole-rats encompasses virtually all of the neocortex normally devoted to vision. These findings indicate that major cortical remodeling has occurred in naked mole-rats, paralleling the anatomical and behavioral specializations related to fossorial life.

Animals↗

PubMed2002

Motor learning-dependent synaptogenesis is localized to functionally reorganized motor cortex.

The regional specificity and functional significance of learning-dependent synaptogenesis within physiologically defined regions of the adult motor cortex are described. In comparison to rats in a motor activity control group, rats trained on a skilled reaching task exhibited an areal expansion of wrist and digit movement representations within the motor cortex. No expansion of hindlimb representations was seen. This functional reorganization was restricted to the caudal forelimb area, as no differences in the topography of movement representations were observed within the rostral forelimb area. Paralleling the physiological changes, trained animals also had significantly more synapses per neuron than controls within layer V of the caudal forelimb area. No differences in the number of synapses per neuron were found in either the rostral forelimb or hindlimb areas. This is the first demonstration of the co-occurrence of functional and structural plasticity within the same cortical regions and provides strong evidence that synapse formation may play a role in supporting learning-dependent changes in cortical function.

Animals↗