Midline thalamic nuclei have prominent connections with limbic structures and are thought to play important roles in affective behaviors and in functions that involve interactions between hippocampus and medial prefrontal cortex. By examining the activity of neurons in the medial mediodorsal, central medial, reuniens, and rhomboid nuclei we hope to elucidate the specific contributions of these nuclei to adaptive goal-directed behavior.
For instance, previous work in our lab has shown that lesions of the mediodorsal nucleus (MD) produce delay-dependent impairment of delayed matching and non-matching (DNMTP) to position tasks while larger lesions involving adjacent midline (M) and rostral intralaminar (IL) nuclei produce delay-independent impairment of these tasks, comparable to the effects of prefrontal lesions. Our work has revealed a wider range of response types than we observed in parallel studies of prefrontal cortex. In general, thalamic neurons exhibited higher levels of activity and PETH patterns that were not as sharp as those found in prefrontal cortex. The results of our studies are consistent with the hypothesis that the medial thalamus plays an active role in shaping response properties of prefrontal cortex.