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Ramping single unit activity in the medial prefrontal cortex and ventral striatum reflects the onset of waiting but not imminent impulsive actions.

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Donnelly, Nicholas A 
Robbins, Trevor W 
Dalley, Jeffrey W 


The medial prefrontal cortex (mPFC) and ventral striatum (VS), including the nucleus accumbens, are key forebrain regions involved in regulating behaviour for future rewards. Dysfunction of these regions can result in impulsivity, characterized by actions that are mistimed and executed without due consideration of their consequences. Here we recorded the activity of single neurons in the mPFC and VS of 16 rats during performance on a five-choice serial reaction time task of sustained visual attention and impulsivity. Impulsive responses were assessed by the number of premature responses made before target stimuli were presented. We found that the majority of cells signalled trial outcome after an action was made (both rewarded and unrewarded). Positive and negative ramping activity was a feature of population activity in the mPFC and VS (49.5 and 50.4% of cells, respectively). This delay-related activity increased at the same rate and reached the same maximum (or minimum) for trials terminated by either correct or premature responses. However, on premature trials, the ramping activity started earlier and coincided with shorter latencies to begin waiting. For all trial types the pattern of ramping activity was unchanged when the pre-stimulus delay period was made variable. Thus, premature responses may result from a failure in the timing of the initiation of a waiting process, combined with a reduced reliance on external sensory cues, rather than a primary failure in delay activity. Our findings further show that the neural locus of this aberrant timing signal may emanate from structures outside the mPFC and VS.



impulsivity, neurophysiology, nucleus accumbens, rat, visual attention, Action Potentials, Animals, Area Under Curve, Choice Behavior, Conditioning, Operant, Impulsive Behavior, Linear Models, Male, Microelectrodes, Neurons, Prefrontal Cortex, Principal Component Analysis, Rats, Reaction Time, Ventral Striatum

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Eur J Neurosci

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Blackwell Publishing Ltd
Medical Research Council (G1000183)
Medical Research Council (G0701500)
Medical Research Council (G0001354)
Wellcome Trust (093875/Z/10/Z)
This research was funded in part by a Medical Research Council grant to J.W.D. (G0701500) and by a joint award from the Medical Research Council (G1000183) and Wellcome Trust (093875/Z/10/Z) in support of the Behavioural and Clinical Neuroscience Institute at Cambridge University. N.A.D. was funded by the University of Cambridge School of Clinical Medicine MB/PhD Program. The authors would like to thank Alan Lyon and David Theobald for assistance with histology, Tim Harris and the Applied Physics and Instrumentation Group at HHMI Janelia Farm for providing electrodes, Ken Harris and the Klustateam at UCL for providing software for spike detection and sorting, and Tahl Holtzman for technical assistance with training in surgical procedures.