|Reference code: ||PT/FB/BL-2008-127.02|
|Location: ||Arquivo PCA - Pasta 6/2008|
|Role of medial prefrontal cortex and secondary motor cortex withholding impulsive action|
|Publication year: ||2009|
Impulse control - withholding short term actions to achieve longer term goals - is an important facet of goal-directed behavior. Frontal cortex has been hypothesized to exert top-down inhibition of impulsive actions, but little is known about the nature of the neural signals responsible for such control. To address these questions, we have developed a novel impulse control task in rats and begun to investigate the causal involvement and neural correlates of frontal cortical areas.
In the impulse control task, subjects interact with a waiting port and a reward port. While waiting, two tones are generated, the first at a fixed short delay (0.4 s) and the second at a longer random delay (exponentially-distributed, min. 0.7 s). Responses after the first tone garner a reward, but the amount is 3-4 times larger after the second tone. A minimum trial onset interval was set so that waiting time did not affect trial rate. Thus, to maximize reward, subjects must withhold responding to the first tone and respond to the second.
This task produces three trial types: “failure” to wait for the first tone, “impatient” responses after the first tone and “patient” responses after the second tone. The delay of the second tone was titrated to achieve 30% patient responses (approx. 2 s mean). The timing of impatient responses varied randomly from trial to trial, approximating the distribution of second tone delays.
First, to test for areas that may be causally involved in impulse control, we infused muscimol locally to inactivate medial and dorsomedial frontal cortex (mPFC and M2). Inactivation of regions within these areas indeed led to a decrease in the waiting time and a decrease in the patient trials.
Second, to characterize neural signals related to impulse control, we made single-unit recordings from mPFC and M2 neurons, testing for signals that correlated on a trial-by-trial basis with waiting time on impatient trials. Approximately 12% of neurons in dorsomedial frontal cortex (28/238 neurons) showed activity that correlated with and predicted waiting time. We observed nearly equal proportions of positive and negative correlations.
Waiting-predictive neurons showed a variety of time courses of activity. The most frequent one was a phasic signal locked to waiting-port entry, but other neurons showed ramping activity peaking at waiting-port exit. Waiting correlated activity sometimes even occurred a few seconds before waiting port entry.
These results establish a task suitable for studying impulse control, suggest the involvement of dorsomedial frontal cortex in this function, and reveal properties of single neural activity that may be responsible for top-down control of impulsive action.
|Accessibility: ||Document exists in file (poster)|
|Secondary author(s): |
|Costa, G., Vicente, M., Mainen, Z.|
|Document type: |
|Murakami, M., Costa, G., Vicente, M., & Mainen, Z. (2009). Role of medial prefrontal cortex and secondary motor cortex withholding impulsive action. Program No. 281.10/EE116. 2009 Neuroscience Meeting Planner. Chicago, IL: Society for Neuroscience, 2009. Online. |
|Indexed document: ||No|
|Keywords: ||Impulsivity / Decision-making / Brain activity|