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Longitudinal Growth Curves of Brain Function Underlying Inhibitory Control through Adolescence
Ordaz SJ, Foran W, Velanova K, Luna B

The ability to stop a compelling but inappropriate response in favor of an optimal planned response is essential to ?executive? control of behavior.  For example, it can be difficult to stop the impulse to attend to a long awaited text alert and wait for a safe time to look at it.  This is one of the hardest abilities to master and underlies impulsivity. Developmentally, it has been widely shown that we continue to improve in our ability to suppress our responses through adolescence.  What is not well known is what aspects of brain function, whose structure is changing through development, can account for greater impulsive behavior in children and teens. 

Working with her mentor, Dr. Bea Luna, and colleagues in the Department of Psychiatry's Laboratory of Neurocognitive Development, Dr. Ordaz used functional Magnetic Resonance Imaging (fMRI) to measure how brain function changed when trying to stop an unwanted response as subjects aged from childhood to adulthood.  Subjects were told to simply not look at a suddenly appearing light in the periphery and to instead look in the mirror location.  This is very hard to do and there is nothing you can learn to make it easier.  The investigators found that different aspects of brain function changed through development.  From childhood to adolescence the prefrontal cortex, a part of the brain that is engaged when we do very difficult planning, decreased its engagement. This reflects how this task becomes easier as we grow older and therefore we rely less on prefrontal function. Importantly, it shows that adolescents engage prefrontal cortex similarly to adults when successfully stopping an inappropriate response, further debunking the notion that a slow maturing prefrontal cortex underlies adolescent behavior.  However, while adolescents commit fewer errors than children, they still commit more errors than adults. The researchers found that another part of the brain that is also in the frontal region, the anterior cingulate cortex (ACC), continued to increase its participation when errors were committed all the way through adulthood.  The ACC has been well-identified as supporting our ability to monitor our performance and to become engaged particularly when we commit errors so as to prevent future mishaps. The ACC was engaged predominantly in adulthood, and the magnitude of its activity was related to the proportion of errors committed.

Taken together, these results provide new insights into how aspects of impulsivity improve with development and their implications to different stages of growth.  Children have a difficult time stopping unwanted responses and can only successfully do this by engaging the executive part of the brain that adults would engage for more difficult tasks.  Adolescents are qualitatively different in that they engage executive prefrontal cortex just like adults when they successfully inhibit an inappropriate response. However, they continue to show limitations in integrating the errors that they commit resulting in a greater overall number of inhibitory errors.  These results may help us understand why adolescents can so often behave in a controlled manner like adults and then make poor decisions very impulsive.  Adolescence is a time of increased sensation seeking but also a time for vulnerability to mental illness.  Being more impulsive can assist in sensation seeking, which is an adaptive process towards adult independence. However, sensation seeking can lead to risk taking, which can undermine survival. Importantly, this change in brain mechanics from adolescence to adulthood could trigger or bring forth impairments that could lead to mental illness.

Contributors:
Sarah J. Ordaz, PhD; William Foran, MS; Katerina Velanova, PhD; Beatriz Luna, PhD (Departments of Psychology and Psychiatry, University of Pittsburgh)

The results of this investigation were published in Journal of Neuroscience.  Click here for a link to the abstract.