A neural pathway for the shift response in the cat

The shift response (McIlwain effect) was elicited by moving a large grating situated greater than 15 degrees from the conventional receptive field center (RFC). We examined the change in the amplitude of the shift response induced by placing a steady target on the RFC or the RF surround. We found that appropriate stimulation of the RFC or the RF surround will increase and inappropriate stimulation will decrease the amplitude of the shift response in a graded manner. The amplitude of the shift response was not correlated with the maintained activity but was correlated with the transient peak firing rate which is evoked by flashing the enhancing stimulus. A shift stimulus which elicits a strong shift response can be blocked by inappropriate stimulation. The results suggest that the shift signal is modulating a tonic signal which is present in the RF. Because the shift response is a transient excitation, we suggest that the shift response results from a disinhibitory process. A possible neural pathway for the shift response is presented.