Supplementary Figure 11: Proposed scheme for active dendritic integration contributing to mixed network representations and sensorimotor behavior.

a, Illustration of nonlinear mixing of spatially segregated multi-modal inputs in L5 pyramidal neurons through active dendritic integration. Above, inputs carrying whisker location information are shown as received by the tuft regions of L5 pyramidal neurons through long-range synaptic inputs from sources like motor cortex (M1) or posteriomedial nuclei in the thalamus (PoM) (schematic shows an example input with location tuning of ~10°). Below, inputs carrying touch information, including the identity of whisker that contacted the object, received predominantly at the proximal dendritic regions of the L5 neuron from sources like the ventral posteriomedial thalamic nucleus (VPM) and from neuronal populations in layers 4 and 2/3 of the principle column corresponding to that whisker (schematic shows a C3 whisker representation for example). Dashed line represents weak long-range synaptic inputs from sources like motor cortex (M1) or posteriomedial nuclei in the thalamus (PoM) to proximal regions. Coincident tuned inputs to both regions (distal and proximal) during active touch by the preferred whisker (C3) at the preferred location (~10°) enables the otherwise restricted back-propagating action potential (bAP) to evoke a long-duration, Ca²⁺ - plateau potential in the distal dendrites. This results in a nonlinear increase in high-frequency bursts of action potentials in somatic output. Thus, the neuron generates a nonlinearly mixed selectivity to the two input modalities, whisker location (10°) and whisker touch (C3 touch). This manifests as a somatotopic map gain modulated by whisker location. b, Network impact, active dendritic integration in a population of L5 neurons results in nonlinearly mixed selectivity to various combinations of whisker angle and whisker touch. Mixed tuning to whisker identity (somatotopy) and whisker location is shown by 3-D surface plots pseudocolored to reflect neuronal output intensity (increasing from blue to red). Such a distributed population forms a high-dimensional basis network that effectively represents object location suitable for a linear read-out by various downstream areas. The resulting activity pattern (e.g. mapping to motor co-ordinates) from an example linear sum is depicted in a potential downstream neuron⁵. c, Illustration of the behavioral result of the neuronal and network level consequences of active dendritic integration. The sensory-motor transformation produces motor related activity in downstream regions that drives whisking patterns that are dependent on the sensory environment.