Figure 8. Local disinhibition of M1 neurons at P12 unmasks twitch-related activity.

(a) Left: Coronal section showing CO staining around the S1/M1 boundary. Middle: Fluorescent image of the same section showing the spatial extent of bicuculline diffusion (blue). White arrow indicates the location of an electrode shank in M1 (red). Right: Illustration of the histological sections at left to show the boundaries of S1 and M1, the laminar structure of each area, and a reconstruction of the location of the microsyringe needle immediately lateral to the recording electrode. Middle, bottom: Experimental timeline. (b) Recording sites (black bars) and diffusion boundaries (blue ovals) for all six saline injections (top) and five bicuculline injections (bottom) depicted in the horizontal plane. The 6th bicuculine injection is shown in the coronal section in (a). All recording sites were within the forelimb representation of M1; diffusion boundaries were largely restricted to M1. (c) Top: Adjusted r² values for twitches (y-axis) and wake movements (x-axis) for each isolated M1 unit before (Pre) and after (Post) injection of saline. Bottom: Same as above, but for bicuculline group. (d) Mean (±SEM) adjusted r² values for twitches (blue) and wake movements (red) before (Pre) and after (Post) injections of saline or bicuculline. * significant difference from Pre (p<0.0125). (e) Percentage of M1 neurons that were wake-responsive (red), twitch- and wake-responsive (purple), and twitch-responsive (blue) during the Pre and Post periods in the saline and bicuculline groups.

Figure 8—figure supplement 1. Representative M1 neural activity before and after injection of saline or bicuculline at P12.

(a) Representative data depicting 20 s periods of active sleep (blue) and wake (red) before (Pre, top) and after (Post, bottom) injection of bicuculline into M1. The data depicted are forelimb movements (twitches: blue ticks; wake movements: red ticks), unit activity within the forelimb representation of M1, and rectified EMGs from contralateral forelimb and nuchal muscles. Each row of depicts unit activity for a different neuron. (b) Perievent histograms of firing rate (spikes per s, sps) for representative M1 neurons triggered on twitches (blue) and wake movements (red) before (Pre) and after (Post) injections of saline (left) or bicuculline (right). Conventions as in Figure 2c. Insets in the top left corner show each neuron’s mean waveform (black line) ±standard deviation. Vertical scale bar = 20 μV; horizontal scale bar = 0.2 ms.