4). On some occasions the monkeys would have numerous ‘eye-closed’ periods of short duration or only a few eye-closed epochs of extended selleck chemical duration. It was notable that the vast majority of the Type 1 neurons described here had regular firing patterns during sleep, as illustrated for a typical single neuron in Fig. 8. The same property was described by Rolls et al. (2003) for single neurons in the subgenual cingulate cortex BA25 during periods of eye-closure. However, of note is that a few

Type 1 cells showed minor variations in the fine temporal patterning of neuronal firing during some ‘eyes-closed’ epochs, with some exhibiting ‘burst-like’ responses. The quantitative areal distribution of cell Types 1, 2 and 3 neurons in mPFC are given in Table 2 (see also Fig. 1C–E). Finally, it was not possible to ascertain unequivocally whether the neurons being studied electrophysiologically were excitatory projection pyramidal cells or local circuit inhibitory neurones. However, the likelihood is that most of the recorded cells were pyramidal projection neurons

as the spike durations were typically greater than 1.2 ms, which is highly characteristic see more of cortical pyramids (Rolls et al., 2003). The principal results of this study indicate that there are two populations of neurons throughout the monkey mPFC that significantly altered their firing rates when the subjects ‘closed’ or ‘opened’ their eyes. Type 1 cells (8.4% of all cells recorded) significantly increased their firing rate when the monkey became drowsy or closed its eyes, whilst Type 2 cells (1.8%) significantly decreased

their firing rate on eye-closure. Together these electrophysiological cell types represent a modest population (10.2%) of all the mPFC neurons screened in this study. Histological reconstructions confirmed that the cells studied electrophysiologically were in BAs 9, 10, 13 m,14c, 24b (dorsal anterior cingulate cortex) and 32 (pregenual cingulate cortex in primates), GBA3 with many of the recorded cells being located in the deep layers of the cortex (see Fig. 1C–E). A previous paper from our laboratory reported that neurons in BA25 (subgenual cingulate cortex) of the macaque mPFC also significantly increased their firing rates when monkeys went to sleep (Rolls et al., 2003). Of note is that comparable to the neurons reported here, the cells studied by Rolls et al. (2003) did not respond to gustatory, olfactory and most visual stimuli. Rolls and colleagues also presented evidence of four neurons in the orbitofrontal cortex (BA13) responding in a similar manner. The present study thus confirms and extends to further areas of mPFC the observations of the earlier companion paper. Taken together these two studies indicate that there are distributed populations of neurons throughout the mPFC of monkeys that selectively respond to being either ‘asleep’ or ‘awake’.