Behavioural examination of the role of the thalamic reticular nucleus in attention

Abstract

The ability to selectively attend to aspects of the environment which signal opportunity or danger, while marginalising irrelevant stimuli is critical to an animal’s survival. With finite cognitive resources, the brain must dedicate resources to only those stimuli that are biologically significant. Incoming thalamic information must therefore be filtered. The thalamic reticular nucleus has long been considered critically involved in modulating thalamic sensory processing. Sharing connections with both the thalamus and cortex, it is ideally located to modulate the transfer of pertinent incoming sensory information. This thesis sought to determine the functional role of the thalamic reticular nucleus in attentional processes by combining lesion techniques and well established behavioural paradigms. Chapter 3 examined the role of visual thalamic reticular nucleus lesions on performance in a two-alternative forced choice reaction time task when auditory distractors were presented. No effect of the lesion was found. Chapter 4 examined excitotoxic lesions of thalamic retlcular nucleus on performance in the 7-stage attentional set shifting task. No effect of lesion on performance was found. Chapter 5 examined mediodorsal thalamus and rostral thalamic reticular nucleus lesions on performance in the attentional set shifting task. Despite strong connectivity with prefrontal regions known to be involved in this task, there was no effect of either lesion. Finally, chapter 6 examined the effects of reducing dopamine input into the thalamic reticular nucleus on a two alternative forced choice reaction time task. Following bilateral lesions the animals were impaired in the re-orientation of attention – suggesting a critical role for both the thalamic reticular nucleus and dopamine in attentional processes. Taken together, these results suggest that while the thalamic reticular nucleus is involved in attention, it is not involved in every aspect.