Attentional orienting is impaired by unilateral lesions of the thalamic reticular nucleus in the rat

The thalamic reticular nucleus (TRN) has been implicated in attentional pro cesses based on its anatomical, electrophysiological, and neurochemical rel ationships with the sensory nuclei of the thalamus and corresponding sensor y areas of cortex. This study examined the possibility that the TRN is invo lved in covert orienting of attention. Attention can be summoned to a spati al location in the absence of an overt orienting response. The reaction tim e to a visual target is faster when attention has been drawn to the locatio n of the target by a preceding cue in that location (valid cue) compared wi th when the cue misdirects attention (invalid cue) away from the location o f the subsequent target. This reaction time difference is referred to as th e "validity effect." Rats were trained to perform such a reaction time task with visual cues and targets presented in poke holes to either side of the rat's head, which had to be maintained centrally and still. If the rat mad e an overt orienting response to the cue, the trial was aborted. Unilateral lesions were made by injection of ibotenic acid in the TRN. After surgery, there was no bias apparent in their responding; they were as likely to ini tiate responses and were equally accurate to either side. There was, howeve r, a complete abolition of the validity effect for responses to contralater al targets. The data are discussed in terms of a role for the TRN in attent ional processing.