_<5-l5 0 15 30 45 ffl 75 90 -15' 0 15 'io' 45 60 75 ' 90 Time (s) Time (s)

FIGURE 14.4 Example of a type 1 neuron from the lateral agranular cortex that was excited on compound, but not simple stimuli. For this rat, the short fixed interval was 10 sec and the long fixed interval was 40 sec. The time on the abscissa represents time from stimulus onset. The two horizontal lines in each graph represent the 95% confidence limits of the baseline firing rate. Bin width = 1 sec. (Reprinted from Pang, K.C., Yoder, R.M., and Olton, D.S., Neuroscience, 103, 615-628, 2001. With permission.)

fixed interval, possibly due to the fact that recordings were obtained on probe trials and participants may be somewhat uncertain of the end of the short fixed interval.

In summary, recordings of lateral agranular neurons in the frontal cortex support the view that this area is important in divided attention. The most common response pattern was one in which cells responded at the time that divided attention is most necessary (i.e., simultaneous presentation of both stimuli). These neurons may allow attention to be switched rapidly between stimuli so that clock pulses can be efficiently collected in the respective accumulators for each stimulus. When these cells are damaged, as in frontal cortex lesions, the participant may be unable to switch attention between tasks and becomes focused on only one of the stimuli, subsequently timing only the attended stimulus, even though multiple stimuli are presented. Although this interpretation is consistent with the results from rats with lesions of the frontal cortex, alternative interpretations exist, and some of these are explored in the next section.

14.4.2 Alternative Explanations

In this section, we entertain some alternative explanations for the response pattern of type 1 neurons and suggest some directions for future research. The two obvious a)

Simple Short b)

Simple Long

Simple Long

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