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1 Centre for Neuroscience, University of Alberta, Edmonton, Alberta, Canada; Visual Sciences Group, Australian National University, Canberra, ACT, Australia
2 Department of Psychology, University of Alberta, Edmonton, Alberta, Canada; Centre for Neuroscience, University of Alberta, Edmonton, Alberta, Canada
* To whom correspondence should be addressed. E-mail: dwylie{at}ualberta.ca.
The pretectal nucleus lentiformis mesencephali (LM) and the nucleus of the basal optic root (nBOR) of the avian accessory optic system (AOS) are retinal-recipient visual nuclei that are involved in the analysis of optic flow that results from self-motion, and in the generation of the optokinetic response. Neurons in these nuclei show direction-selectivity in response to large-field motion, and are tuned in the spatio-temporal domain. In addition to retinal afferentation, both the nBOR and LM receive afferents from the Wulst, which is thought to be the avian homologue of primary visual cortex. We examined the effects of Wulst electrical stimulation on the activity of LM neurons and recorded the directional and spatio-temporal tuning of LM neurons in pigeons before, during, and after the Wulst was temporarily inactivated by lidocaine injection. In response to Wulst electrical stimulation, LM neurons showed either short latency excitation followed by longer latency inhibition (W+ cells), or only a longer latency inhibition (W- cells). The average response latencies for W+ and W- cells were 13.5ms and 28.3ms, respectively. The effects of Wulst stimulation did not correlate with either the directional or spatio-temporal tuning of the LM neurons. Injection of lidocaine into the nBOR reduced the longer latency oscillations of W+ and W- cells. When the Wulst was temporarily inactivated by lidocaine neither the directional nor spatio-temporal response properties of LM neurons were affected. The possible functions of the projection from the Wulst to the LM are discussed.
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