Credit: courtesy: 2010 Sinauer Associates, Inc.

An Immature Frontal Lobe Impacts Decision Making. Will This Influence The Tsarnaev Jury?

May 7, 2015

The issue of the development of an adolescence brain is suddenly thrust into the limelight during one of Boston’s most significant court cases in history…the federal trial of Dzhokhar Tsarnaev, the admitted Boston Marathon Bomber from the 2013 attacks.

His defense team is trying to spare the now 21-year old from the death penalty, during the penalty phase of the trial, so they’ve brought in witnesses to testify about partial brain development that could affect reasoning and decision making.

Dr. Marisa Silveri, Director of the Neurodevelopmenal Laboratory on Addictions and Mental Health at McLean Hospital in Belmont and Associate Professor of Psychiatry at Harvard Medical School, discussed the topic with Morning Edition host Bob Seay  saying that in the past,  the age of 18 was the considered adulthood, but neuro-imaging by researchers is showing otherwise.

At the Neurodevelopmental Lab at McLean, researchers are studying the brain to better understand the neurobiology of decision making, which often gets to the root of “what were you thinking” decision making.

Silveri says one of the things they’ve learned in the last decade, “there are a number of organizational events in the brain that are really doing their biggest work during that second decade of life, roughly from age 10 to early 20s, a time that overlaps with the need for improved decision making."

It’s happening on several fronts of the brain, both in terms of the structure of the brain, how much grey matter, how many neurons there are, how well is the brain connected, what is the connectivity through white matter or axons that connect the neurons, to give the brain better cell-service,” says Silveri.

Research is showing if you ask an adolescent or even an adult, the age-old phrase, “What were your thinking, ”they most likely know the right answer.  But  when you then  ask , "Why did you do it"….many adolescents might say “I don’t know,” and she says the decision making machinery in the brain is trying to come together to make those differences."

She says changes in the brain are still fine tuning from the ages of 18-24, the period of life-emerging adulthood.

Silveri says the frontal lobe of the brain is where executive functions sit and integrates with the rest of the brain.  Research shows the frontal lobe of the brain is developing and sculpting during this period of adolescence, and it’s more sensitive and vulnerable to substance use and abuse and could impair the decision making  process.  Court proceedings have revealed Tsarnaev was a habitual marijuana user.

She says if your teenager blames a mistake on an "immature frontal lobe, don't let them get away with it, because she says, "if they know to say that phrase they should know better."


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