| I conducted system identification analysis of neuronal responses to bimanual stimulation in the second somatosensory cortex (SII) in order to examine each SII neuron as an information processing device and identify it structurally and functionally. Oriented bars stimulated the distal pads of digits 2, 3, and 4 on each hand, and neuronal activity in SII responding to the tactile stimulation was monitored via single-unit recording. Regression analysis was conducted to investigate SII neurons' receptive field structures and bimanual responsiveness, and information theoretic analysis was performed to quantify SII neurons' ipsilateral and contralateral information processing. I also examined orientation selectivity of SII neurons and the attentional modulation of neuronal activity for orientation discrimination in SII.; Most SII neurons were significantly responsive to both ipsilateral and contralateral stimulation, and exhibited a continuum of bimanual responsiveness and a variety of receptive field structures. SII neurons generally showed high degrees of linearity in their responses to bimanual stimulation, but interactions between inputs from multiple digits contributed significantly to the response variability attributable to tactile stimulation for a subpopulation of SII neurons. A majority of SII neurons processed information about both ipsilateral and contralateral stimulation although they processed more information about contralateral stimulation. They showed stronger orientation selectivity for contralateral stimulation than for ipsilateral stimulation while exhibiting similar orientation tuning on both hands. SII neurons' bimanual responsiveness and information processing were substantially affected by the behavioral state of the animal, and neuronal discriminability between two orientations in SII was significantly enhanced when tactile bars were attentively processed for orientation discrimination.; The studies described in this thesis thus demonstrate that SII neurons process information about both ipsilateral and contralateral stimulation with dynamical bimanual responsiveness that reflects the attentional state of the animal. The results of the studies suggest that SII constitutes an important cortical area in the main somatosensory pathway for object recognition where neurons construct feature-based, non-isomorphic representations that reflect behavioral goals. |
