The modulation of cortical dendrites during sensory perception and learning

Abstract

Sensory perception arises in the cortex by integrating external information from the environment with internal representations and the current brain state. This process is supported by the structure of the neocortex and the organisation of excitatory inputs onto its core computational element: the pyramidal neuron. In layer 2/3 pyramidal neurons, external (feedforward) information mainly target the somatic region, while internal (feedback) information runs through layer 1 and lands onto distal tuft dendrites. Cortical dendrites have active properties that could be important for sensory processing and could provide a cellular mechanism to support the flexibility of sensory representations during learning. In this thesis, I addressed the role of L2/3 pyramidal neuron dendrites during sensory perception and learning in three parallel studies that investigated: 1) how inputs from another sensory area affect early stages of sensory processing; 2) the modulation of sensory processing in dendrites of the auditory cortex following fear conditioning; 3) changes in dendritic activity during perceptual learning of an auditory discrimination task. To tackle these questions, a combination of two photon Ca2+ imaging and whole cell patch clamp electrophysiology in vivo, together with behavioral testing and optogenetics manipulation, was used. The results presented here confirm that dendrites encode sensory information and show that they can undergo plastic changes during learning. The findings also illustrate the existence of compartmentalised activity in L2/3 pyramidal neurons and of a cellular mechanism for the control of action potential generation that involve dendritic integration. The results presented in this thesis highlight the importance of the upper layers of the cortex for flexible sensory representation through the integration of feedback and feedforward information.