RAPID COMMUNICATION Nonlinear Processing of Tactile Information in the Thalamocortical Loop

Ghazanfar, Asif A. and Miguel A. L. Nicolelis. Nonlinear prorons following stimulation of single-whisker versus coincicessing of tactile information in the thalamocortical loop. J. Neurodentally displaced multiwhisker stimuli. physiol. 78: 506–510, 1997. Rats explore tangible objects in a manner such that, at any given moment in time, multiple facial M E T H O D S whiskers simultaneously contact the surface of the object. Although both thalamic and cortical neurons responsible for processing such Processing of tactile information was quantified by simultanetactile information have large, multiwhisker receptive fields, it reously recording the sensory responses of populations of layer V mains unclear what kinds of computations can be carried out by neurons, located in SI, and neurons located in VPM. Recordings these neuronal populations when behaviorally relevant multiwere obtained 1 wk after chronic implantation of two electrode whisker stimuli are used. By simultaneously recording the activity arrays, each of which contained 16 Teflon-coated stainless steel of up to 78 cortical and thalamic neurons per animal, we observed microwires (50 mm diam, NBlabs, Dennison TX). Electrode arrays that the magnitude of sensory responses and the spatial spread of consisted of two rows, separated by 1 mm, of eight microwires ensemble activity increased in a nonlinear fashion according to the spaced 200 mm apart. This allowedÇ2 mm of tissue to be sampled extent and spatial orientation of the multiwhisker stimuli. Supralinin each structure. During surgery, neural activity was recorded and ear responses were seen more frequently with vertically than with RFs were mapped to ensure proper placement of electrodes in layer horizontally oriented stimuli. These data suggest that thalamocortiV of SI and in VPM. Histological analysis of Nissl-stained sections cal interactions in the rat somatosensory system can generate comwas used to confirm electrode placement for all animals. Realplex spatial transformations of multiwhisker stimuli that go beyond time characterization of single neurons and recording of neuronal the classic inhibitory interactions previously observed. ensemble activity were carried out with the use of a multineuronal acquisition processor (MNAP, Spectrum Scientific, Dallas TX). Ensemble recordings were carried out in lightly anesthetized ani-