Multisensory enhancement in the optic tectum of the barn owl: spike count and spike timing.
Yael Zahar, Yoram Gutfreund
Last modified: 2008-05-13
The specialization of the barn owl in hunting small prey in dimly lighted and acoustically noisy environments provides us with an attractive model for studying cross-modal integration. In the present work we studied responses of multisensory neurons in the barn owl optic tectum (the avian homolog of the superior colliculus) to visual, auditory and bimodal stimuli. We specifically focused on responses to long sequences of repeated stimuli. We first report that bimodal stimulation tends to elicit more spikes than in the responses to its unimodal components (a phenomenon known as multisensory enhancement). However, this tendency was found to be history-dependent, multisensory enhancement was mostly apparent in the first stimulus of the sequence and to a much lesser extent in subsequent stimuli. Next, a vector strength analysis was applied to quantify the phase locking of the responses to the stimuli. We report that in a substantial number of multisensory neurons responses to sequences of bimodal stimuli elicited spike trains that were better phase locked to the stimulus than spike trains elicited by stimulating with the unimodal counterparts (visual or auditory). Therefore, multisensory enhancement can be manifested in phase locking to the stimulus rather than more spikes.