|Ph.D Student||Netser Shai|
|Subject||Novelty Response and Habituation in the Barn Owl|
|Department||Department of Medicine||Supervisor||Professor Yoram Gutfreund|
|Full Thesis text|
The most basic form of stimulus selection is based on the history of the stimuli the animal was exposed to. Stimuli that are repetitively presented are less likely to induce responses, while novel stimuli are selected for responses. At the behavioral level, this process is known as habituation while at the neural level it is known as Stimulus Specific Adaptation (SSA). Whether the two phenomena are directly linked is unknown. In the current study I aimed to find this link in the auditory system of the barn owl. Long lasting adaptation was found in both OT and E - the midbrain and forebrain stations of the tecto-fugal pathway. In the OT, the long lasting adaptation was found to be stimulus specific, occurring even with ISIs as long as 60 seconds. A comparable long lasting adaptation was not detected in the main auditory pathway. Thus, the observed long lasting SSA was correlated on a global level with behavioral habituation. In the second part of this work, we showed that Pupil dilation responses (PDRs) can be induced by microstimulation of OT. As the PDR is known as a novelty response, this result suggests that the OT is also involved in novelty detection. When performing low level microstimulation just prior to an already habituated auditory stimulus, the response tended to be significantly larger compare to the response for both stimuli separately. This priming was a specific effect since congruency between the site of microstimulation in the tectal map and the location of the auditory stimulus resulted with stronger sensitization of the PDR. The results clearly emphasize OT contribution to temporal saliency, but on the same time demonstrate the contribution to saliency in space. In the third part of this work, we simultaneously recorded PDRs and neural activity of OT and E neurons in order to assess the correlation on a trial by trial basis. Surprisingly, ongoing activity just prior to stimulation was significantly correlated with the PDR. We next studied the nature of this ongoing activity by recording simultaneously from two electrodes in OT. The correlation was significantly stronger for close sites compared to distant ones. OT ongoing activity was also significantly correlated with E ongoing activity. To summarize, the results presented in this thesis suggest that the tecto-fugal pathway of the barn owl as a whole, and the OT in particular, encodes salient events in both space and time.