Comparative analysis of orientation maps in areas 17 and 18 of the cat primary visual cortex following adaptation.

Object orientations in the visual field are columned into specific orientation domains in the primary visual cortex [area 17 (A17) and area 18 (A18)] of cats. At the single-cell level, adapting A17 neurons to a non-preferred orientation (adaptor) shifts their preferred orientation either towards the adaptor (attractive shift) or away from it (repulsive shift). As A17 and A18 are reciprocally connected, we sought to determine how changes in preferred orientations in A18 neurons are correlated with changes recorded in A17 anesthetised cats. To this end, we simultaneously traced populations of neurons in A17 and A18, using intrinsic optical imaging, before and after long (12 min) and short (3 min) adaptations. The comparison of A17 and A18 maps pre-adaptation and post-adaptation showed that variance in shift amplitudes is greater in A18 than A17 for short adaptations. Our results indicate a rapid reconfiguration of functional maps that may spread to many cortical areas.

Adaptation shifts preferred orientation of tuning curve in the mouse visual cortex.

In frontalized mammals it has been demonstrated that adaptation produces shift of the peak of the orientation tuning curve of neuron following frequent or lengthier presentation of a non-preferred stimulus. Depending on the duration of adaptation the shift is attractive (toward the adapter) or repulsive (away from the adapter). Mouse exhibits a salt-and-pepper cortical organization of orientation maps, hence this species may respond differently to adaptation. To examine this question, we determined the effect of twelve minutes of adaptation to one particular orientation on neuronal orientation tuning curves in V1 of anesthetized mice. Multi-unit activity of neurons in V1 was recorded in a conventional fashion. Cells were stimulated with sine-wave drifting gratings whose orientation tilted in steps. Results revealed that similarly to cats and monkeys, majority of cells shifted their optimal orientation in the direction of the adapter while a small proportion exhibited a repulsive shift. Moreover, initially untuned cells showing poor tuning curves reacted to adaptation by displaying sharp orientation selectivity. It seems that modification of the cellular property following adaptation is a general phenomenon observed in all mammals in spite of the different organization pattern of the visual cortex. This study is of pertinence to comprehend the mechanistic pathways of brain plasticity.