Summary: Researchers have identified the roles five sub-areas of the prefrontal cortex make in movement decisions.
Source: University of Freiburg.
Whether the brain responds to an external stimulus or not depends significantly on the balance between areas of excitation and inhibition in the prefrontal cortex (PFC). Synaptic connections in the front of the cerebral cortex enable the brain to make a conscious decision on whether to react to a stimulus with movement or not. However, the roles of the individual regions in the PFC and how they work together in this decision-making process were unknown until now. An international team led by Stefanie Hardung from the research group of Professor Ilka Diester, a member of Bernstein Center Freiburg and the Cluster of Excellence BrainLinks-BrainTools, has now identified the roles five subareas in the prefrontal cortex play in making decisions on movement. Their results were now published in the journal Current Biology. This study may be of particular significance for the further investigation of impulse control disorders.
“We might compare these regions of the prefrontal cortex with a traffic light” says Stefanie Hardung. “Specific subareas of the PFC are responsible for inhibition, while others take care of movement preparation and excitation.”In their experiment, the researchers employed a framework in which they trained transgenic rats in proactive and reactive stopping: “Reactive stopping refers to a situation in which the animal stops in reaction to an external signal. Proactive stopping, on the other hand, develops according to the internal goals of the subject.” In their specific setup, the rats were trained to press a lever and to stop if a specific signal was given. Another signal indicated that the rat was supposed to keep pressing the lever. With the help of optogenetics, the research group was able to deactivate specific genetically altered brain cells using light. The scientists systematically switched off certain subareas of the PFC to test the influence of these respective regions on the decision-making process. In addition, optogenetics enabled the group to compare the results with the behavior of the same animals when all areas were intact.
The deactivation of specific PFC regions significantly altered the performance of the animals: The inhibition of regions in the infralimbic cortex (IL) or the orbitofrontal cortex (OFC) impeded the ability of the rats to react to external signals. Deactivation of the prelimbic cortex (PL), on the other hand, caused a premature reaction in the majority of the rats. Furthermore, the researchers employed electrophysiological measuring methods and observed that neuronal activity in the PL significantly decreased prior to the premature reactions when all regions were intact.
These insights support the hypothesis that the infralimbic cortex and the prelimbic cortex play an opposing role to that of the orbitofrontal cortex: While the IL and the PL direct proactive behavior in reaction to external signals, the OFC controls reactive behavior. Thus, their study might serve as a basis for new approaches in the investigation of impulse control disorders such as attention deficit hyperactivity disorder (ADHD) or obsessive-compulsive disorders (OCD). “Optogenetic approaches are less harmful to the animals than surgical or pharmacological interventions,” Hartung explains. “They allow us to deactivate different brain areas swiftly and reversibly without affecting circuit connectivity. Thus, our animal model might serve as an adequate framework for investigating impulse control disorders.”
Funding: The work was funded by the Mead Johnson Nutrition.
Source: Michael Veit – University of Freiburg
Image Source: NeuroscienceNews.com image is credited to Michael Veit.
Original Research: Abstract for “A Functional Gradient in the Rodent Prefrontal Cortex Supports Behavioral Inhibition” by Stefanie Hardung, Robert Epple, Zoe Jäckel, David Eriksson, Cem Uran, Verena Senn, Lihi Gibor, Ofer Yizhar, and Ilka Diester in Current Biology. Published online February 9 2017 doi:10.1016/j.cub.2016.12.052
[cbtabs][cbtab title=”MLA”]University of Freiburg “Traffic Light in the Brain.” NeuroscienceNews. NeuroscienceNews, 11 February 2017.
<https://neurosciencenews.com/pfc-external-stimuli-6102/>.[/cbtab][cbtab title=”APA”]University of Freiburg (2017, February 11). Traffic Light in the Brain. NeuroscienceNew. Retrieved February 11, 2017 from https://neurosciencenews.com/pfc-external-stimuli-6102/[/cbtab][cbtab title=”Chicago”]University of Freiburg “Traffic Light in the Brain.” https://neurosciencenews.com/pfc-external-stimuli-6102/ (accessed February 11, 2017).[/cbtab][/cbtabs]
A Functional Gradient in the Rodent Prefrontal Cortex Supports Behavioral Inhibition
•Optogenetic PL/IL inhibition promotes/suppresses early responses, respectively
•Optogenetic VO inhibition results in more late releases and longer reaction times
•mPFC/OFC contribute in a more proactive/reactive way, respectively
•Specialized neuronal subpopulations contribute to behavioral inhibition/execution
The ability to plan and execute appropriately timed responses to external stimuli is based on a well-orchestrated balance between movement initiation and inhibition. In impulse control disorders involving the prefrontal cortex (PFC), this balance is disturbed, emphasizing the critical role that PFC plays in appropriately timing actions. Here, we employed optogenetic and electrophysiological techniques to systematically analyze the functional role of five key subareas of the rat medial PFC (mPFC) and orbitofrontal cortex (OFC) in action control. Inactivation of mPFC subareas induced drastic changes in performance, namely an increase (prelimbic cortex, PL) or decrease (infralimbic cortex, IL) of premature responses. Additionally, electrophysiology revealed a significant decrease in neuronal activity of a PL subpopulation prior to premature responses. In contrast, inhibition of OFC subareas (mainly the ventral OFC, i.e., VO) significantly impaired the ability to respond rapidly after external cues. Consistent with these findings, mPFC activity during response preparation predicted trial outcomes and reaction times significantly better than OFC activity. These data support the concept of opposing roles of IL and PL in directing proactive behavior and argue for an involvement of OFC in predominantly reactive movement control. By attributing defined roles to rodent PFC sections, this study contributes to a deeper understanding of the functional heterogeneity of this brain area and thus may guide medically relevant studies of PFC-associated impulse control disorders in this animal model for neural disorders.
“A Functional Gradient in the Rodent Prefrontal Cortex Supports Behavioral Inhibition” by Stefanie Hardung, Robert Epple, Zoe Jäckel, David Eriksson, Cem Uran, Verena Senn, Lihi Gibor, Ofer Yizhar, and Ilka Diester in Current Biology. Published online February 9 2017 doi:10.1016/j.cub.2016.12.052