The hippocampus plays a crucial role in the perception of uncertainty

The hippocampus, an area of the brain essential to memory and learning, code the degree of uncertainty related to whether or not a reward. This role has been highlighted by Giovanna Vanni-Mercier and colleagues at the Cognitive Neuroscience Center (CNRS / Université Lyon 1), in collaboration with the medical team épileptologie the Neurological Hospital of Lyon. Published on 22 April 2009 in the Journal of Neuroscience, this work shed new light on how our brain extract and process the relationships observed in our environment.

Present in all living beings, the circuit said the reward is a neural circuit that "reward" with a feeling of pleasure and satisfaction with the core functions for survival (food, reproduction, response to aggression). In mammals, particularly primates, it promotes not only the behaviors associated with basic needs, but also more complex behaviors like learning and motivation. It allows you to detect the stimuli associated with reward and to predict their occurrence based on past experience. Faculty that facilitate decision making. This reward system consists of dopamine neurons in the deep regions of the brain and their connections with other brain areas.

The role of the hippocampus in memory and learning has long been known. But never his involvement in the treatment of the statistical properties of the award had previously been studied. To do this, researchers have recorded in patients with epilepsy the activity of their hippocampus healthy (1) while they learned to estimate the probabilities of gains under different virtual machines. Result, when the third roll of the slot machine has stopped, indicating if the test had been a winner or not, the hippocampus gave a transient signal whose amplitude varies with the probability of obtaining a monetary award . The signal has a maximum amplitude when the uncertainty of obtaining a reward had also been possible. It is something of a warning signal that allows the subject to increase alertness and attention.

The hippocampus, therefore, a code transient signal, and subsequently, the strength of the link between the stimulus (here, the slot machine) and the event associated with it (here, the gain). It differs from the dopaminergic neurons that encode the uncertainty of this association supported by a signal emitted during the expectation of reward. What may well serve as this signal? First, it can play a complementary role to that of dopaminergic neurons in the associative learning to connect a stimulus to an event associated with it (accordingly). The signal of uncertainty expressed by dopaminergic neurons facilitate motivation and exploration, while the hippocampus may direct attention to the consequence of the event announced. The latter would thus, in a process of feedback, updating the strength of the link between stimulus and result in a second time, the behavior appropriate to the situation. Furthermore, this coding may be involved in other functions of the hippocampus known but unknown mechanism, for example, the probability or the classification of transitive reasoning (roughly speaking, this amounts to assume that if A> B , B> C, and C> D, then B> D).

This work highlights the fundamental role of the hippocampus in making rational decision in a context of uncertainty. They bring new elements to better understand how the brain retrieves and processes information and interrelationships found in the environment.

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