Churchland lab

Brains live inside bodies that move around, and this simple fact means a lot of extra work for neural circuits. Imagine you are following a flying bird with your eyes. If your brain needs to know how fast the bird is moving in space, it needs to account for the fact that the image of the bird on your retina is altered by the movements of your eye. A Cosyne Workshop talk by Larry Abbott provides some new insights into the neural circuits that make this possible. He did this work with a number of collaborators, including Anne Kennedy (right) and Nate Sawtell, both known among the cosyne crowd for their innovative approaches to complex problems.

The model organism the group used to tackle this problem was the electric fish, which detects its dinner (fish and bugs) by sensing the electrical signals they create in the water. The challenge for the fish is that it sends out electrical pulses to accomplish this, altering the electrical signals that its sensory organs experience, just like in the case of vision and the bird above.

The key advance Larry talked about (part of which is published here) is that they made a large-scale realistic model that included 20,000 neurons. These were manufactured based on response properties of a smaller number of real neurons observed in a laboratory setting. Their model solved the problem by constructing a negative image of the signal sent out, and then subtracting it from the detected inputs. A key test for the model is to see what happens when the animal sends a descending command to emit the pulse, but this never actually happens (as if the fish were paralyzed, for instance). When this happens, the signal needed to be subtracted out changes. Once conditions are brought back to normal, a signature of this adjusted signal is evident. This was true in both the model and the fish.

An exciting future direction, to my mind, will be to see the degree to which the circuits that accomplish this behavior are similar in humans. Because subtracting out the consequences of movements if fundamental for all organisms, similar strategies could be evident even in very different species.