Figure 6.

Different inputs to the sensory laminar neocortex may activate different modes of laminar engagement. The laminar schematic shown here illustrates L2/3, L4, and L5/6. Sinusoids depict gamma rhythms in each layer. The light gray sinusoid in L2/3 depicts oscillatory input from L4. Signal flow is depicted by green arrows. The size of the arrow denotes the relative strength of connection. (A) A strong sensory stimulus arrives from the thalamus to L4, producing a gamma rhythm (black trace). The rhythm in L4 is directly coherent with the L5 output layer. We propose that sensory information carried in the gamma frequency goes directly from L4 to L5/6. In contrast, the rhythm in L2/3 is at a lower gamma frequency than that in L4 and L5/6. Although immediate sensory information may not be processed directly by L2/3, the interaction of different gamma rhythms is predicted to create plasticity between L2/3 and L4. (B) In a more difficult task, such as a search task that requires context matching, moderate sensory input engages gamma rhythms in L4 that lock in frequency to L2/3. Sensory information is transmitted from L4 to L2/3. In contrast to A, L2/3 has a direct effect on L5/6 output. (C) Plasticity between E‐cell populations in L4 and L2/3 (denoted by the larger green arrow) is predicted to recruit activity in L2/3 that can increase the output of L5/6.