Recordings In The Frontal Cortex

In an attempt to better understand how frontal cortex neurons contribute to attention and timing, we recorded from neurons in the lateral agranular region of the frontal cortex during the STP procedure (Pang et al., 2001). The lateral agranular region of the frontal cortex was selected for recordings because rats with damage to this area have impaired performance on compound, but not simple trials of the STP procedure, suggesting a deficit in divided attention (Olton et al., 1988). Rats were trained on the STP procedure using 10 sec as the fixed interval for one stimulus (short stimulus) and 20 or 40 sec as the fixed interval for the second stimulus (long stimulus). Electrophys-iological data were acquired and analyzed from probe trials exclusively. Peri-event time histograms were constructed for the onset of each stimulus. Confidence intervals were determined on the basis of neuronal activity during the 10 sec prior to stimulus onset.

In behavioral analyses, peak time for the short stimulus was similar on simple and compound trials, and peak time for the long stimulus was similar on simple and compound trials (Figure 14.3). Similar peak times on simple and compound trials for each stimulus demonstrate that timing two stimuli simultaneously was just as accurate as timing a single stimulus, and support the idea that normal rats can divide attention and accurately time two stimuli simultaneously.

14.4.1 Evidence for Divided Attention Neurons

Task-sensitive neurons were those cells having firing rates that exceeded the 95% confidence intervals for at least 4 consecutive seconds. A total of 125 neurons were recorded in the frontal cortex, and 65 of these were task-sensitive neurons by our definition. Of the task-sensitive neurons, four general firing patterns were observed. Type 1 cells (60%) responded to simultaneous presentation of both stimuli on compound trials, but not to stimuli on simple trials (Figure 14.4). Type 2 cells (10%)

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