Local Cortical Processing Research Articles

Distortions of visuotopic map match orientation singularities in primary visual cortex.

The map of orientation columns in primary visual cortex (V1) is known to show strong local distortions, with a generally smooth progression of orientation preference across extended regions of cortex, interrupted by sharp jumps (fractures) and point singularities. The map of visual space on V1, in contrast, has been assumed to be locally smooth and isotropic. We find, on the contrary, that the map of visual space on cat V1 shows strong and systematic local distortions in register with inhomogeneities in the orientation map, with the rate of receptive field movement across cortex being largely proportional to the local rate of change of orientation. This suggests possible systematic local variations in the functional connectivity of short-range lateral connections that underlie local cortical processing.

Transient Increase of AMPA and NMDA Receptor Binding in the Barrel Cortex of Mice after Tactile Stimulation

The effects of sensory stimulation and sensory conditioning upon [3H]MK-801 [(+)-5-methyl-10,11-dihydro- 5H-dibenzo[a,d]cyclohepten-5,10-imine] binding toN-methyl-d-aspartate (NMDA) receptor sites and [3H]AMPA (α-amino-3-hydroxy-5-methylisoxasole-4-propionic acid) binding to AMPA receptor sites were examined in the primary somatosensory (SI) cortex of mice. Following short-lasting unilateral tactile stimulation of a selected row of vibrissae, and tactile stimulation paired with noxious stimulus (the pairing procedure was found to alter cortical representation of vibrissae), in vitro receptor binding autoradiography was performed on the sections of the barrel cortex of mice. One hour after the end of tactile stimulation or training procedure there was an increase of [3H]MK-801 and [3H]AMPA binding in the corresponding row of barrels in layer IV of the SI cortex of adult mice. These effects disappeared 24 h after the end of each experimental procedure. The results suggest that both subtypes of glutamate receptors are regulated in an activity-dependent way and that sensory stimulation transiently modifies local cortical processing.

Plasticity in the barrel cortex of the adult mouse: transient increase of GAD-immunoreactivity following sensory stimulation.

Sensory experience during perinatal life and adulthood modifies physiological and anatomical characteristics of the central nervous system. So far, this phenomenon has been studied in situations of complete or partial sensory deprivation. We here report that increased sensory stimulation, during four days, of a number of whisker follicles on the face of the adult mouse results in an increased immunoreactivity of glutamic acid decarboxylase (the biosynthetic enzyme of the inhibitory neurotransmitter GABA) in the somatosensory cortex of the adult mouse. Effects were limited to a column of tissue corresponding to the representation of the stimulated follicles and lasted two days beyond stimulation. These findings suggest that sensory stimulation transiently modifies local cortical processing.