Proposed Scheme of Afferent Conduction of Active-Touch Signals

<p>Whisking signals (W) are conveyed by the paralemniscal pathway (para) via the POm and are proposed to involve whisking control. Touch signals (T) are conveyed by the extralemniscal pathway (extra) via VPMvl, and are proposed to involve processing of object location (“where”). Combined whisking–touch signals (WT) are conveyed by the lemniscal pathway via VPMdm, and are proposed to involve processing of object identity (“what”).</p

Distributions of Normalized Touch Responses in the Thalamus

<p>(A) TI value of each of the recorded neurons is indicated by a color code on its relative location in the canonical thalamic map defined in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0040124#pbio-0040124-g001" target="_blank">Figure 1</a>D. (B) Distribution of TI in VPMdm ( <i>n</i> = 30), VPMvl ( <i>n</i> = 13), and POm ( <i>n</i> = 24). </p

Distributions of Thalamic Latencies and Durations According to Response Type

<div><p>(A) Latencies from protraction onset to half-peak response of all thalamic neurons during touch trials.</p> <p>(B) Latencies from relevant stimulus (contact time for Touch neurons and protraction onset for the rest) to half-peak response of all thalamic neurons during touch trials.</p> <p>(C) Response durations of individual cells during touch trials, measured from the PSTH, as the period during protraction in which the response was above 0.1 of its maximum.</p></div

Electrode placement and behavioral results.

<p>A, Coronal sections of the rat brain illustrating MD and mPFC electrode placements. The coordinates are based on a standard rat brain atlas <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0050578#pone.0050578-Paxinos1" target="_blank">[58]</a>. The numbers indicate distance in mm from Bregma. MDC, mediodorsal thalamic nucleus, central part; MDM, mediodorsal thalamic nucleus, medial part; Cg1, cingulate cortex, area1; PrL; prelimbic cortex. B, Outcome devaluation test. Devalued, rats received 1 h of unlimited food pellets, same as earned by lever pressing. Non-devalued, rats did not receive any food for 1 h before test. Normalized rate of presses were the ratio of presses under each condition. Error bars indicate SEM.</p

LFP recording in MD and mPFC during behavior.

<p>Representative LFP traces recorded from the four electrodes during the final session. LFPs in the MD exhibit prominent theta band (∼7–8 Hz) oscillations, whereas LFPs in the mPFC show prominent gamma band (∼50 Hz) oscillations.</p

Learning-related modulation in LFP activities.

<p><b>A,</b> Perievent raster plots of representative LFP recording. Both examples display depolarization following reward delivery. B, Perivent histograms of representative LFP recorded from 3 rats during the first training session and the last session (top, MD; bottom, mPFC). LFPs exhibit depolarization (negativity in the extracellular recording) with learning.</p

Dynamic changes in oscillatory activity during learning.

<p>A, Power spectral analysis of theta and gamma oscillations in the MD. Theta band oscillations increased during training, but gamma oscillations did not. First, first session; Last, last (4th) training session. Representative data are shown from one rat with simultaneous MD and mPFC recordings. B, Normalized (% of the first session) power of theta and gamma oscillations in the MD (n = 22) during acquisition. Theta oscillations in the MD increased significantly over time, whereas gamma oscillations did not. Data from all animals are averaged and shown here. Error bars present SEM. C, Power spectral analysis of theta and gamma oscillations in the mPFC. Representative data are shown from one rat with simultaneous MD and mPFC recordings. D, Normalized (% of the first session) power of theta and gamma oscillations in the mPFC (n = 14) during acquisition. There was a significant increase in the gamma oscillation but not in theta oscillations.</p

Neuronal activity in MD and mPFC during acquisition.

<p>A, Left, action potential waveform and distribution of interspike intervals of representative neurons recorded from MD and mPFC. Right, Perievent raster plots of representative neurons. Each row in raster plot represents a single trial. Green line represents time of reward delivery. Reward excited neuron increases firing after the completion of lever press action and delivery of reward. Reward inhibited neuron decreases firing upon the delivery of reward. B, Top, spike density functions of individual neurons that transiently increased (MD n = 42; mPFC n = 28) or decreased (MD n = 32; mPFC n = 17) activity following reward delivery. Each row shows a z-score normalized spike density function for a single neuron. The neurons are sorted by the latency to the maximum or minimum amplitude. Bottom, normalized population firing rate of reward excited and inhibited neurons at the time of reward delivery. Shaded areas indicate SEM.</p

Changes in coherence between MD and mPFC during learning.

<p>A, Left, Overall coherence from two representative electrodes during the first (green) and last (red) session in MD and mPFC. Right, dynamic changes of theta and gamma coherence during 4 sessions of instrumental learning (n = 33 pairs in each session). Error bars represent SEM. B, Left, coherence upon reward delivery measured from activity from two representative electrodes. Right, dynamic modulation of theta and gamma coherence by the reward delivery. Error bars indicate SEM.</p

Theta and gamma frequency oscillations.

<p>(A and C) Perievent spectrograms of representative MD (<i>A</i>) and mPFC <i>(C)</i> LFP during the first (top) and last (bottom) session. MD Theta power is much stronger compare to mPFC. mPFC gamma power is much stronger compared to MD. After learning, gamma power is maximal at the time of reward delivery. (B and D) Changes of normalized power spectra of theta and gamma frequency oscillations in MD (n = 22) <i>(B)</i> and mPFC (n = 14) <i>(D</i>) upon the reward deliver across four sessions. Error bars indicate SEM.</p