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The physiological characteristics and organization of cat primary somatosensory cortex (SI) were studied in electrophysiological and anatomical experiments. In single cell recording experiments, quantitatively controlled mechanical stimuli were used to examine the responses of SI cortical neurons to the velocity component of skin or hair displacement. The firing frequency of most rapidly adapting neurons increased as stimulus velocity was increased. Rapidly adapting neurons were classified based on their response patterns to constant-velocity ramp stimuli. Neurons in these classes differed significantly in sensitivity to stimulus velocity and amplitude, adaptation rate, and spontaneous firing rate. The results suggest that frequency coding of stimulus displacement velocity could be performed by individual SI rapidly adapting neurons, and that the classes of rapidly adapting neurons may play different roles in sensation of tactile stimuli. Tract-tracing experiments were used to investigate the ipsilateral corticocortical connections of areas 3b and 2 in SI. Different patterns of connections were found for these areas: area 2 projects to areas 3b, 1, 3a, 5a, 4 and second somatosensory cortex (SII), and area 3b projects to areas 2, 1, 3a and SII. To further compare the organization of these areas, the thalamic input to the forepaw representation within each area was studied. The forepaw region in area 3b receives thalamic input exclusively from ventroposteriopr lateral nucleus (VPL), while area 2 receives input from VPL, medial division of the posterior complex (PoM), and lateral posterior nucleus (LP). These results suggest that area 2 lies at a higher position in the hierarchy of somatosensory information flow.

Sensory neocortex contains a significant number of inhibitory neurons that use gamma-aminobutyric acid (GABA) as their neurotransmitter. Functional roles for these neurons have been identified in physiological studies. For example, in primary somatosensory cortex (SI), blockade of GABAa receptors with bicuculline leads to expansion of receptive fields (RFs). The magnitude of RF enlargement varies between SIpopulations of GABAergic neurons were identified by labeling specific calcium binding proteins.

L'imagerie optique multispectrale du signal intrinsèque permet d'estimer les variations des paramètres hémodynamiques à partir de la collecte des fluctuations de réflectance, à au moins deux longueurs d'onde, induites par une activation cérébrale. Cette thèse propose une étude méthodologique et instrumentale mais aussi une validation in vivo des développements entrepris. Le calcul des paramètres hémodynamiques nécessite l'application d'une loi de Beer-Lambert modifiée introduisant un terme crucial pour la précision du calcul des variations des paramètres hémodynamiques, le DP, que nous avons estimé par simulation Monte Carlo pour les modèles du cortex somatosensoriel et du bulbe olfactif de rat. Nous montrons ainsi que les variations d'absorption, de diffusion ou d'anisotropie n'influe pas sur les valeurs de DP en dessous de 630 nm, que la géométrie et les propriétés optiques des structures a un impact sur celles-ci. Ainsi, le calcul des DP pour chaque structure cérébrale est indispensable. En outre, le choix des longueurs d'onde d'illumination est décisif et s'apprécie en fonction de deux paramètres, la diaphonie et le séparabilité qui ont été calculés pour déterminer les couples et les triplets de longueurs d'onde optimaux pour l'étude du bulbe olfactif de rat. Il apparaît que les valeurs de séparabilité sont négligeables en raison de la forte absorptivité des tissus biologiques dans le visible et que le choix des combinaisons optimales peut se faire en se basant seulement sur les valeurs de diaphonie. La deuxième étape a consisté à construire un banc d'imagerie multispectrale performant et à le valider ainsi que l'étude méthodologique. Les résultats in vivo montrent une différence flagrante des signaux de réflectance et hémodynamiques entre le cortex somatosensoriel et le bulbe olfactif dont l'origine physique et/ou biologique est discutée. / Multispectral imaging of intrinsic optical signal allows to estimate changes in hemodynamic parameters from the collection of reflectance fluctuations, at least with two wavelengths, induced by cerebral activation. This thesis proposes methodological and instrumental studies but also in vivo validation of developments undertaken. The calculation of hemodynamic parameters requires the application of a modified Beer-Lambert law introducing a crucial term for accuracy of hemodynamic parameters changes calculation, the DP, which had been estimated using Monte Carlo simulation models of the somatosensory cortex and olfactory bulb of rats. We show that the variations of absorption, diffusion or anisotropy does not affect the values of DP, whereas geometry and optical properties of the structures have an great impact on them. Thus, calculation of DP for each studied brain structure is essential. In addition, the choice of wavelength illumination is critical and appreciated in terms of two parameters, crosstalk and separability. Pairs and triplets of optimal wavelengths for rat olfactory bulb study were calculated. It appears that the separability values are negligible due to the high absorptivity of biological tissues in the visible and the choice of optimal combinations can be based only on the values of crosstalk. The second step was to build a bench multispectral imaging performance, to validate it and methodological study. The results show a striking difference hemodynamic and reflectance signals between somatosensory cortex and olfactory bulb, which physical origin and/or biological is discussed.

The corpus callosum, the major interhemispheric fiber tract, mediates communication between homotopic regions within the primary somatosensory cortex (S1). Recently, in 1- to 6-day-old neonatal rats, brief bursts of high-frequency, oscillatory activity - called spindle-bursts (SBs) - were described in S1 following sensory feedback from endogenously generated sleep-related myoclonic twitch movements and exogenously generated peripheral stimulation. To determine whether interhemispheric communication via the corpus callosum modulates the expression of SBs during this early period of development and contributes to cortical organization and plasticity, we investigated the endogenous (spontaneous) expression and exogenous (evoked) activity of SBs in neonatal rats with intact or surgically severed callosal fibers (i.e., callosotomy; CCx). We used Ag/AgCl cortical surface electrodes in the S1-forelimb region of the cortex to measure neurophysiological and behavioral activity in both intact and CCx subjects across the sleep-wake cycle during the first two postnatal weeks of development. Our results demonstrate, for the first time, that the corpus callosum modulates spontaneous and evoked activity between homotopic regions in S1 as early as 24-hours after birth. In addition, CCx disinhibits cortical activity, nearly doubling the rate of spontaneous SBs through, but not after, postnatal day 6 (P6). CCx also significantly and reliably disrupts the evoked response to peripheral stimulation of the forepaw. To examine the role of sleep-related twitches and their associated sensory feedback (SBs in S1) - modulated by the corpus callosum - in cortical development and plasticity, we performed CCx or sham surgeries at P1, P6, or P8, and tested subjects the day of surgery or over the ensuing week of recovery. Regardless of age, CCx immediately disrupted SBs evoked by forepaw stimulation. The P1 and P6 CCx groups exhibited full recovery after one week; in contrast, the P8 group did not exhibit recovery of function, thus indicating an abrupt decrease in cortical plasticity between P6 and P8. Together, these results provide the first evidence that sleep-related myoclonic twitches and the associated sensory feedback in S1 (SBs) contribute to cortical development, plasticity, and recovery of function after interhemispheric communication is disrupted by callosotomy. CCx-induced disinhibition of spontaneous SBs is a transient phenomenon whose disappearance coincides with the onset of increased intrinsic connectivity, establishment of excitatory-inhibitory balance, and diminished plasticity in S1. Our findings indicate that CCx-induced disinhibition of spontaneous twitch-related SBs and disruption of evoked response to peripheral stimulation serve as a bioassay of somatosensory cortical plasticity during the early postnatal period.

Thesis (Ph.D.)--University of Tennessee Health Science Center, 2007. / Title from title page screen (viewed on February 29, 2008). Research advisor: Robert S. Waters, Ph.D. Document formatted into pages (xix, 179 p. : ill.). Vita. Abstract. Includes bibliographical references (p. 152-178).

Thesis (Ph. D.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains viii, 143 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.

Diss. (sammanfattning) Stockholm : Karol. inst., 2002. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2002. / Härtill 4 uppsatser.