Category: Brain Science

We learn from others by observing their actions and the resulting outcomes. That way we’re able to use the experience of others to guide us in areas where we may not have personal experience. Research described in a paper titled “Fictive Reward Signals in the Anterior Cingulate Cortex” (published May 15, 2009 in Science) shows that some brain cells (neurons) in the anterior cingulate cortex carry information about both the potential reward of a particular act and the experienced outcome.

When people think about activity in the brain they usually think about neurons. Neurons are the brain cells that send signals to and receive signals from other neurons. They communicate electrically by supporting electrical impulses known as action potentials. When an action potential reaches another neuron it communicates with it through a special structure known as a synapse, which includes a very small space between the sending and receiving neurons. The action potential causes a chemical, known as a neurotransmitter, to be released from the sending neuron, which then crosses the space in the synapse, and binds to receptors on the receiving neuron where it influences electrical signaling.

Another kind of brain cell known as glia are often thought of as “supporting” cells (glia literally means glue in Greek) and are often ignored when scientists think about how the brain does its signal processing to support, for example, sensation or perception. New research adds to the evidence that glia may be just as important as neurons for signal processing in the brain. The paper “Channel-Mediated Tonic GABA Release from Glia” (published November 5, 2010 in Science) demonstrates that glia are an important source for at least some of the tonic inhibition found through much of the brain.

Tonic inhibition is like keeping the brakes engaged in an automobile that is revved up and ready to go. If you release the brakes, the car is off and running until you brake again. In the brain, many neurons would be revved up and ready to fire a lot of action potentials if the “brakes” weren’t kept on through tonic inhibition. In fact, the loss of appropriate tonic inhibition is one possible reason for epileptic seizures.

In their new paper, the research team demonstrates that the glial cells in a particular part of the brain known as the cerebellum have ion channels (bestrophin 1) that chronically release an inhibitory neurotransmitter (most likely GABA) onto neurons known as granule cells and a particular set of axons known as parallel fibers. The resulting tonic inhibition is clearly in the position to play a significant role in signal processing in the cerebellum. Future research should provide insight into what that role is and if the same or similar mechanisms involving glial cells can account for tonic inhibition in other parts of the brain.

How is it that we recognize a person’s face from every angle? It remains a mystery how the brain does this and it’s been extremely difficult to achieve with computers. A paper published this month provides new insights into how the brain may achieve face identity invariance across different viewpoints.

The paper is titled “Functional Compartmentalization and Viewpoint Generalization Within the Macaque Face-Processing System” and was published November 5, 2010 in Science.

Brain imaging shows that, in non-human primates, there are six discrete areas of cerebral cortex that respond specifically to the sight of faces. Researchers looked closely at the physiology of four of these regions. They found that the two areas on the temporal lobes towards the back of the brain responded to individual views of faces. The area on the temporal lobes about midway between the front and the back of the brain responded vigorously to mirror image views of faces. Finally, the area on the temporal lobes closest to the front of the brain didn’t respond vigorously to any one view of a face but responded consistently to different views of a particular face.

These results, in addition to data on when signals arrive at each area, suggest a hierarchical processing of visual signals from back to front along the temporal lobes that results in identity invariance across different viewpoints. The mirror image responses are particularly intriguing. How are they contributing to signal processing?