A new study explains the link between substance-use disorder and brain functioning.
For the study, the team of researchers led by Rebecca Landes McNamee, assistant research professor of radiology and bioengineering at the University of Pittsburgh used functional magnetic resonance imaging (fMRI) to assess eye movements in adolescents to show that children and adolescents at high risk for developing a substance-use disorder (SUD) tend to show deficits in executive cognitive function (ECF) or frontal brain activation.
"ECF is basically the control centre for governing other cognitive processes. For example, in school, ECF would be engaged in the planning and control process required in answering a question; formulating your response, raising your hand, waiting until you are called upon, and stating your answer," explained McNamee.
"A person with low levels of ECF might blurt out the answer. Another example could be interacting with someone on the playground who upsets you. A person with good ECF will think through the actions and consequences of their behaviour rather than responding rashly. A person with low levels of ECF may respond with violence," she said.
The researchers opted for an antisaccade task to reveal the inhibitory response required in the actions above.
"While this eye-movement task may be more basic in nature than an inhibitory response, it still requires control and response suppression, and is thought to use the same basic mechanisms in the brain as those required in more difficult suppression tasks. As response inhibition is something that may be deficient in high-risk children, we thought this task would be a beneficial way to study the workings of basic mechanisms in the brain," she said.
In the study the scientists used fMRI with 25 adolescents (15 males, 10 females), between the age of 12 to 19 years, during a task that needed the inhibition of an initial eye-movement response as well as a voluntary realignment to an alternate location.
These fMRI findings were grouped into regions of activation: total frontal, parietal, occipital, and temporal lobe.
Besides, the researchers examined each subject's neurobehavioral disinhibition (ND), their ability to control an immediate impulsive response to a given situation, and also determined the drug use/histories.
"We found that individuals who exhibit a high amount of ND - that is, do not have a good ability to manage their impulsive responses - have less brain activity in the frontal cortex, the region of the brain responsible for ECF, during the antisaccade task. In other words, the regions of the brain responsible for these inhibitory processes engaged less energy in individuals with higher ND scores than those with lower ND scores," said McNamee.
She said that usually the development of a normal adolescent involves an increase in the ability to block impulsive responses, which would be shown in an increase in brain activation in areas associated with inhibition.
"Since some of the children show less ability to inhibit responses - observed as higher levels of ND - along with less brain activity in these areas, we can hypothesize that the reason for this is a delay in the development of brain networks associated with inhibition. We cannot say for sure what may cause these deficits, but we suspect it has to do with a combination of genetics inherited from the parents and/or the environment in which the individual was raised," she said.
According to her, one of the key implications of these findings is that behaviours and actions are directly related to brain functioning.
"Teachers, caregivers, and other individuals should understand that each adolescent matures at a different rate; they do not always respond like adults because their brains are not at the same level of functioning as an adult. Responses and behaviours related to a certain situation are less easy for some adolescents to manage than others," she said.
Results of this study are published in the recent issue of Alcoholism: Clinical & Experimental Research.