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  • Final Activity Report Summary - CONTEXTE (Continuous neural tracking of external events: effects of the dynamic properties of spiking responses on context tracking and modulation of plasticity ...)

CONTEXTE Résumé de rapport

Project ID: 511273
Financé au titre de: FP6-MOBILITY
Pays: Spain

Final Activity Report Summary - CONTEXTE (Continuous neural tracking of external events: effects of the dynamic properties of spiking responses on context tracking and modulation of plasticity ...)

What happens in our brain when we explore a sensory context for instance, when we run our fingers along some furniture for the first time and noticing the changes between soft and rough surfaces? When a mammal explores its environment, patterns of electrical activity generated by neurons in the brain area known as the cerebral cortex represent the outside world and underlie sensory perception. Beyond representing specific stimulus features, neuronal responses of sensory regions in the cortex change depending on sensory context, internal brain state and even aspects of stimulus significance (such as novelty or pleasant or noxious associations). The responses themselves can regulate modifications in the underlying neurons. Our laboratory analyses this fascinating interplay by identifying neuronal operations or computations whose function can be characterised in the intact animal, and describing the underlying mechanisms at the level of interactions between neurons and their connections (synapses).

We work in the primary somatosensory (barrel) cortex of the rat, a cortical area that contains a representation of the animal's facial whiskers. Rodents are eminently tactile animals: their whisker system is crucial and provides impressive object location and discrimination abilities. We use insights from the whisker system to formulate hypotheses on how tactile representations might work and get modified in mammalian brains in general, including our own.

During our laboratory's setting up and initial work, and specifically during this project, we have focused on the propagation and dynamics of neuronal responses as an animal explores an environment. In the barrel cortex and many other areas, responses adapt to sensory context: i.e. neurons adjust their response level as a function of contextual factors such as the time over which the stimulus has been explored, the general history of stimulation, etc. The time scale over which adaptation occurs (hundreds of ms to several seconds) corresponds to the period over which the animal experiences a novel environment. Adaptive behaviour is a key part of response dynamics, and a rapid form of plasticity.

Adaptation can play an important role in sensory encoding: adjusting their responses adaptively to stimulus statistics, neurons can quickly improve their ability to represent or encode the scene. This had been shown in the visual and auditory systems. In this project, we have shown for the first time how adaptation affects tactile encoding in barrel cortex. Neurons in barrel cortex adapt their responses to the on-going stimulus distribution, adjusting their response tuning functions to match the scale of variations in the stimulus. This enhances neurons ability to transmit a maintained level of sensory information and may help animals improve their tactile discrimination abilities.

In our analysis, we have used recordings of neural activity in the intact rat and quantitative methods based on various statistical and mathematical tools such as information theory. We have also extended the recordings and methods to sites throughout the somatosensory neural pathway that leads from the whiskers up to the cortex. We are now working on characterising how sensory responses propagate along the pathway, as well as on identifying the locations where various kinds of adaptation arise.

We are also working on analyses of the underlying microscopic mechanisms that determine response dynamics in the somatosensory pathway. We combine several levels of description. In addition to our recordings in live rats, we use computer modelling to simulate how specific known properties of neurons can generate the phenomenon observed in the intact animal, and we isolate brain slices where we perform detailed measurements of the properties of neurons and their connections. Combining these techniques, we are making progress in determining how neuronal response dynamics are transformed across stages of the pathway.


Maria Victoria SANCHEZ-VIVES
Tél.: +34-9659-19368
Fax: +34-9659-19547