Figure 2. Neural activity in VPM thalamus during three behavioural states.

A, a continuous 50 s trace of the first principal component of neural ensemble activity in VPM across quiet, whisker twitching and whisking behaviours. B, responses of single VPM neurones to the presentation of two infraorbital nerve stimuli with an interstimulus interval of 50 ms (stimuli presented at bold dotted lines; horizontal dotted lines indicate baseline firing level). C, average peristimulus time histograms (PSTHs) of neural activity in VPM neurones before and after one stimulation of the infraorbital nerve (note that the peaks of the responses to the stimulus have been truncated so the lower-magnitude activity can easily be seen; stimuli presented at bold dotted lines; horizontal dotted lines indicate baseline firing level). D, rasters showing the activity of four single units in VPM during each behaviour. Bursting activity is identified by asterisks above each raster. E, amount of partial directed coherence observed during each of the three behaviours. The top panel is for partial directed coherence from SI to VPM, the bottom panel from VPM to SI. Colour indicates the intensity of the coherence, white indicating none and yellow indicating the highest level of coherence. F, cumulative sum of amount of cortical area activated by a single infraorbital nerve stimulus. Values are normalized to the maximum activated area in the quiet state. From Nicolelis & Fanselow, 2002. Reproduced with permission (http://www.nature.com.nn).