Individual brain cells can make a bigger contribution to behaviour and are capable of more computations than previously thought, suggest three papers published in Nature. The mammalian brain faces a serious resource problem - there aren't enough neurons to have one responsible for every single perception, behaviour or memory. To increase its storage capacity the brain is thought to use overlapping patterns of activity across many interconnected neurons instead, but new research indicates that this underestimates the part individual cells can play.
Using a new method for stimulating neurons in the part of the mouse brain involved in whisker-touch with light, a team led by Karel Svoboda demonstrates that brief bursts of activity in a few neurons are all it takes to trigger learning and decision-making. In another study, Michael Brecht and Arthur R. Houweling managed to pin down the influence of a single cell on a rat's ability to sense touch. By electrically stimulating neurons in the barrel cortex they found that slightly increasing a neuron's activity directly affected whether or not rats reported a touch-like sensation. In a third technically impressive study, Karel Svoboda and Christopher D. Harvey zoomed in on the individual connections - or 'synapses' - between neurons. Each neuron has many synapses, scattered across its branch-like dendrites. As an animal learns, synapses become stronger or weaker, changing the pattern of connections thought to store information. Previous experiments showed that stimulating a single synapse can change its strength, but computer models predict 'crosstalk' between neighbouring synapses. Harvey and Svoboda confirmed this prediction, showing that the neighbours of recently strengthened connections were themselves easier to potentiate. This hints at a kind of neuronal filing system, in which connections relevant to similar kinds of behaviour might cluster together.
These papers add to our growing understanding of the complex processing that can go on within a single cell, and raise interesting questions about how widespread these effects are.
Karel Svoboda (Howard Hughes Medical Institute, Ashburn, VA, USA)
Michael Brecht (BCCN Humboldt-University, Berlin, Germany)
Abstracts available online:
(C) Nature press release.
Message posted by: Trevor M. D'Souza