Limited plasticity of difference neurons in the visual cortex and hippocampus in rabbits during the oddball (random substitutions) test.

The activity of 41 visual cortex neurons and 20 hippocampal field CA1 neurons was studied in rabbits during application of the oddball stimulation paradigm using color stimuli of different intensities. Among these cells, about one third were plastic cells (34% of cortical cells and 37% of hippocampal cells). These neurons showed significant increases in late responses, at times 200-500 and 200-1000 msec for visual cortex neurons and 300-550 msec for hippocampal neurons, to rare deviant stimuli of lesser intensity as compared with responses to the frequent standard stimuli of greater intensity. The initial peak of the response (40-120 msec), the "difference discharge," remained stable in responses to deviant and standard stimuli throughout the experiment. It is suggested that the strengthening of the late components of neuron responses to rare deviant stimuli (limited plasticity) reflects inclusion of the mechanisms of the orientational reflex.