Figure S1. A schematic diagram illustrating the effect of mechanical stimulation of the periphery on activity in early somatosensory cortex. When the distal tip of a digit (e.g. D1 or thumb) is stimulated with a gentle pressure stimulus (green flash in figure), the mechanoreceptors underneath the stimulus site become active, which, via direct afferent projections to the brainstem and then the somatosensory thalamus, eventually stimulates neurons in a circumscribed region of early somatosensory cortex (large black arrow), known as the D1 hot spot (green circle in cortex). The somatosensory cortex is topographically organized so that the D2 hot spot, namely the cortical region directly activated by stimulation of D2 or index finger, lies adjacent to the D1 hot spot. Activity in the D1 hot spot activates, via local, within-area intracortical connections (black arrow in cortex), the neighboring D2 hot spot (purple circle). The activity in the D2 hot spot resulting from the stimulation of D1 (more specifically, activity in the D2 hot spot normalized to that of the D1 hot spot, or the D2/D1 activity ratio as illustrated) is a functional measure of the strength of local, intracortical connectivity within somatosensory cortex. Similarly, the ratio of D1/D2 activity in response to D2 stimulation (not illustrated) measures intracortical connectivity as well. Note that for the sake of illustration, various components of the figure are not drawn to scale.

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