Sustained activation and executive control in the avian prefrontal cortex.

We review our studies examining neural correlates of directed forgetting and executive control in the avian prefrontal cortex. One of the fundamental forms of executive control is the ability to selectively filter information, retaining that which is critical for the current purposes and discarding that which is not. In our first experiment, we trained birds on a directed-forgetting version of a delayed matching-to-sample task. Following a sample stimulus, a bird heard either a remember tone indicating that a memory test would follow, or a forget tone indicating that no memory test would be given. We found that neural activity in the avian prefrontal cortex increased when the bird was told to remember, and decreased when the bird was told to forget. Behavioral probe tests confirmed that the animals were forgetting on forget trials. Although the sustained activation observed on remember trials and the absence of such activation on forget trials could be a code of remembering and forgetting the sample stimulus, it could also be a code of the possibility of obtaining a reward. To address this issue we conducted a second study in which we used three cues: remember, forget, and forget-reward. The forget-reward cue instructed the subject to forget the sample yet at the same time provided a free reward. Neural activity on forget-reward trials matched that on remember trials tentatively indicating that the sustained activation on remember trials might be a reward code rather than a sample stimulus code. Behavioral probe tests, however, failed to indicate that the animals were forgetting on forget-reward trials, and hence it still is possible that the sustained activation could be a code for memory of the sample stimulus.