European Commission logo
français français
CORDIS - Résultats de la recherche de l’UE
Contenu archivé le 2024-05-30

Brain states, synapses and behaviour

Final Report Summary - BRAINSTATES (Brain states, synapses and behaviour)

The first electroencephalogram recordings of electrical activity from the brain of awake animals and humans revealed patterns of spontaneous activity that were correlated to different behavioral states but seemed unrelated to direct sensory input. These patterns of activity are now termed brain or cortical states. Changes in brain state have been observed in awake mammals. In mice, during periods of quiet wakefulness, large amplitude slow fluctuations are observed in the membrane potential of cortical neurons (a quiet or relaxed state). During periods of movement or arousal, slow oscillations are disrupted and replaced by smaller amplitude faster activity (the active brain state). In this project we examined the cellular and network mechanisms generating cortical states and the role of the cortex in somatosensory processing, synaptic transmission and behavior.

We used head-restrained awake and anesthetized mice. We monitored mouse behavior with movement sensors and capacitance contact sensors alongside high speed filming. To monitor cortical activity we made extracellular action potential, local field potential and membrane potential measurements of cortical neurons in vivo. Identified cortical cell types were targeted either with in vivo two-photon microscopy of fluorescently labeled neurons in transgenic mice, or with optogenetic stimulation during recording or blind recordings with post-hoc biocytin staining.

Dual whole-cell recordings from layers 2/3 and 5 in awake mice have shown laminar differences in the dynamics of cortical activity across layers during different brain states, with layer 5 neurons firing earlier during slow oscilaltions and more during periods of movement. Two-photon recordings from layer 2/3 pyramidal neurons identified higher firing cortical excitatory pyramidal neurons that express higher levels of the immediate early gene cfos. Moreover fos expressing layer 2 pyramidal neurons were observed to have distinct sensory response properties and thalamo-cortical functional wiring.

To measure the impact of cortical states on monosynaptic transmission we have developed multiple (2 to 4) two-photon targeted whole-cell recordings from identified cell types in vivo. This technique allowed us to both record and stimulate neighboring identified and synaptically connected cells. We have identified unitary excitatory and inhibitory synaptic connections between cortical neurons and compare their properties during periods of quiescence and network activity and their impact on local network activity. In vivo cortical connections showed low overall connectivity with more reciprocal connections than expected, but were less reliable and had lower levels of paired pulse depression than prior cortical slice studies.

To examine the impact of cortical activity and brain states on behavior we developed new trained behavioral tasks for head-restrained mice. Mice were trained to lick for a water reward in response to a tactile or thermal stimulus, and reach and press a sensor with their forepaw following a brief tactile stimulus. This allowed us to record and manipulate cortical activity in behaving mice and link cortical activity to tactile and thermal perception and movement of the forepaw. We showed that cortical ongoing and sensory evoked activity is required for thermal perception and voluntary control of forelimb movement.