Article of the Month, December 2017 (Sompolinsky's lab)

November 30, 2017

Optimal Degrees of Synaptic Connectivity

Authors: Litwin-Kumar et al. (Sompolinsky's lab)
Published in Neuron on March 2017   
About half of the neurons in the human brain -- 50 billion or so -- are
located in the cerebellum, a brain region responsible for, among other
things, fine motor control. Remarkably, however, each of these neurons
receives on average only four inputs that convey information about the
external world. Analogous regions in other animals, including the insect
mushroom body, responsible for odor learning, share a similar
organization. Litwin-Kumar et al. investigated how these large but very
sparsely connected systems are nonetheless capable of supporting complex
behaviors. They developed a measure of the dimensionality of the neural
responses in each area -- related to how many different combinations of
sensory inputs a population of neurons can represent -- and found that
the dimension is maximized when the number of connections per neuron is
small. The optimal number of connections from the theory precisely
matches the true value from anatomy, suggesting that evolution has
optimized these brain areas to produce high-dimensional representations
of the sensory environment.
AOM 12/2017 fig1