Seminar Series

Cellular mechanisms for sensory perception

Converging evidence suggests that perception relies on top-down inputs (or feedback) from higher order brain regions to primary sensory regions. However, there is as yet no clear explanation of how this top-down influence operates at the mechanistic level. It has been proposed that top-down influence depends on the active properties of the apical dendrites of pyramidal neurons. My recent study revealed that active calcium currents in the apical dendrites of a subset of layer 5 (L5) pyramidal neurons in primary somatosensory cortex (S1) in mice was correlated with the threshold for perceptual detection of whisker deflections (Takahashi et al., 2016). Manipulating the activity of apical dendrites shifted the perceptual threshold, demonstrating that perceptual process depends critically on activation of the apical dendrites of L5 pyramidal neurons in S1. L5 pyramidal neurons in S1 are categorized into two subtypes based on their output targets, i.e, cortico-cortical (CC) and cortico-subcortical (CS) neurons. More recently, I have found that when the whisker stimulus exceeded perceptual threshold, calcium currents in the dendrites of CS neurons were stronger and more reliable than those of CC neuron. The increase in dendritic activity in CS neurons was dependent on the behavioral-context and causally linked to the animal’s perceptual performance. These results suggest that the dendritic calcium currents serve as a cellular mechanism that gates top-down signals into the subcortical information stream, which then shapes the perceptual threshold for detecting sensory stimuli. Takahashi N, Oertner T, Hegemann P, Larkum M. Active cortical dendrites modulate perception. Science 354:1587−90 (2016)