Even neurons have favori...( dual neurons. When monkeys are trained...)

In the current study, the researchers explored how prefrontal neurons become attuned to quantitative categories. They trained two monkeys to release a lever when the number of dots from one to five -- that appeared on a computer screen matched the number they had seen a second earlier. The animals learned to hold onto the lever if the quantities didn't match, receiving juice as a reward for correct answers. To make sure the monkeys weren't cheating -- picking up on low-level visual cues instead of actually judging quantity -- the researchers randomly varied the locations, sizes and other features of the dots across several trials. While the monkeys were performing this number task, the investigators recorded the electrical activity of 352 randomly selected neurons in the part of the prefrontal cortex where sensory information is processed.

They found that the activity of at least a third of the neurons varied along with the number of dots seen, and their consistent patterns for a given number also generalized across widely varied displays, signaling that the cells were indeed tuning to quantity. Each cell showed a peak of activity for one of the five quantity categories and a systematic trailing-off as the numerical discrepancy between its preferred number of dots and the number presented on a given trial increased.

The researchers speculate that the neurons chose favorite quantities as a result of learning to perform the task. Individual cells become highly specialized as they adapt to experience, participating in multiple networks that can perform many different tasks.

When brain activity for the preferred quantity dropped significantly, there was an increased probability for the monkey to give the wrong answer, providing further confirmation that the measured brain acti
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Contact: Jules Asher
NIMHpress@nih.gov
301-443-4536
NIH/National Institute of Mental Health
5-Sep-2002