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Moving in the right direction

One of the characteristics of animals is that they can choose where to go: migrating caribou move on to new pastures, a tomcat makes the rounds to mark its territory, or a man goes to the bar for a drink. This process, known as spacial navigation, is quite complex. Eric Burguière and the rest of Laure Rondi-Reig's team, at the Physiology of Perception and Action laboratory (LPPA)1 have been studying this particular issue.2 Spatial navigation requires collecting information about the outside world: the animal must develop a representation of its environment and its own position in it, and then control its muscles in such a way as to move towards the desired location.

 Rondi-Reig's team has demonstrated that a particular cellular phenomenon in the brain's cerebellum is required for mice to follow an optimal trajectory: Long-Term Depression (Ltd) of the parallel fiber-Purkinje cell synapses. Synapses are the junctions where neurons interact, and parallel fibers and Purkinje cells are types of neurons found in the cerebellum. This Long-Term Depression refers to the synaptic transmission becoming less efficient. Learning and memory may well be based on changes in the efficiency of synaptic transmission. The Department of Neuroscience in Rotterdam (Netherlands) has bred a strain of mice without this cerebellar Ltd. Burguière has tested these mice in two different types of mazes. The first was an open space where the mice had to find a particular location to get their reward. After a few trials, normal mice went straight to the right location. On the other hand, the mice with no cerebellar Ltd wandered around, often in the wrong direction, but eventually found their way. The second maze had a series of narrow passages, forcing the mice  to move in straight lines. The task was therefore reduced to finding the right location without having to worry about controlling their trajectory. The mice with no cerebellar Ltd performed as well as the others. What does this show? In the absence of Ltd, the animals know where they want to go, but given freedom of movement, cannot follow the best trajectory: They make mistakes and are unable to make the continual adjustments required to follow a direct path.

 This study moves us one step forward in our understanding of brain functions. Spatial navigation, and the continual motor adjustments required for everyday life are some of the first processes to be affected by ageing, or neurodegenerative diseases. Research, like spatial navigation, requires analysis of the context to identify the optimal direction to proceed. Rondi-Reig's team is doing just that.

Alex Edelman

Notes :

1. Laboratoire de Physiologie de la Perception et de l'Action. Joint lab: CNRS / Collège de France.
2. E. Burguière et al., “Spatial navigation impairment in mice lacking cerebellar LTD: a motor adaptation deficit?” Nat Neurosci. 8 (10): 1292-4. 2005.

Contacts :

Laure Rondi-Reig
Collège de France, Paris
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