Active Dendritic Currents Gate Descending Cortical Outputs in Perception - Medical Science Assignment Help

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The output of cortical columns is routed to different downstream targets via distinct pathways: cortico-cortical and cortico-subcortical. It is as yet unclear what roles these pathways play in perception, and which cellular and circuit mechanisms regulate their gating. We recently showed that activation of the apical dendrites of layer 5 (L5) pyramidal neurons correlates with the threshold for perception, but these neurons come in two classes that target either other cortical or subcortical areas. In the present study, we took advantage of transgenic mouse lines for these L5 subclasses to determine their relative contribu-tions to the perceptual process. We found that the activation of apical dendrites in neurons of the somatosensory cortex, which project to subcortical regions, almost exclusively determined the detection of tactile stimuli in mice. Our results suggest that dendritic activation drives context-dependent interactions between cortex and subcortical regions, including the higher-order thalamus, superior colliculus and striatum, which are crucial for perception.

Sensory perception is highly context dependent1,2 . Recent stud-ies have shown that sensory perception depends on a bio- physical mechanism built in at the cellular level to the apical dendrites of deep (L5) cortical pyramidal neurons3–5 . Underlying this mechanism is the generation of Ca2+-dependent dendritic pla-teau potentials, often referred to as dendritic Ca2+ spikes, which drive these neurons to fire bursts of high-frequency action potentials (APs)6,7. It has been suggested that the dendritic Ca2+ spike serves as a mechanism to associate feed-forward sensory signals with con- textual information carried by long-range projections, enabling context-dependent sensory coding in cortical pyramidal neurons3,8

Apical Ca2+ currents of PT, but not IT, neurons modulate the per- ceptual threshold. Our data showed that active Ca2+ currents in the apical dendrites of PT neurons, but not IT neurons, were strongly correlated with the animals’ perceptual behavior. To test the cau- sality of the Ca2+ currents during perceptual detection, we exam- ined the behavioral performance of the mice while upregulating the dendritic activity of L5 neurons in S1.

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