Dr. Grossi's Blog


Dr. Philip Grossi
Tuesday, 31 May 2011

Distractibility is a daily experience we all share with our family, friends, patients, or colleagues. What's more, when attempts are made to capture this phenomenon with questionnaires, a high degree of heritability is discovered.  This has led to the hypothesis that the phenomenon is brain-based. Now come the researchers Kanai, Dong, Bahrami, and Rees who studied this exact problem and published in the May 5, 2010 issue of The Journal of Neuroscience.

Survival in everyday life requires ignoring irrelevant distracting information and at the same time focusing on selected relevant information. Selecting incoming information depends on two distinct yet complementary mechanisms.  A voluntary mechanism directs attention to events relevant to current goals, but also attention can be attracted by salient stimuli in the environment. If the first is insufficient, then the second dominates, leading to distractibility and difficulty in maintaining attention on the task at hand.  This, in turn, leads to accidents and decreased productivity. 

Ability to maintain attention in the presence of distractors can be measured by a variety of tools, among which is the Cognitive Failures Questionnaire (CFQ), whose reliability and validity is established.  The test demonstrated that distraction is highly heritable in a study of >3000 Dutch adolescent monozygotic and dizygotic pairs, where CFQ scores mediated by genetic factors was >50% and that therefore CFQ scores were mediated by brain differences and therefore by brain structure in >50% of cases.

The above researchers performed three experiments a description of which goes beyond what I plan to describe due to time and space.  They were trying to determine whether inter-individual variability in daily examples of distractibility had a corresponding brain structure. The results of these studies are summarized below. 

illustration to distractibility blogTheir first experiment found that variability in regional grey matter density of the left superior parietal lobe (SPL) predicted an individual's distractibility in everyday life.  Their second experiment validated this connection and confirmed that the SPL was involved in the top-down control of distractibility as well as suppression of salient task-irrelevant stimuli, which is confirmation of previous work by de Fockert et.al. in the early 2000s.  A truly interesting implication of the current reported study is that grey matter density in the left SPL was larger in the more highly distractible individuals.  This positive correlation is startling because it has always been assumed that larger cortical volume or greater grey matter density is associated with superior performance.  This study shows that greater grey matter density in adulthood is associated with poorer performance. 

What is the explanation for this conundrum?  Perhaps the most straightforward,  though not the only one, is that during adolescence the human cortex undergoes a process of pruning, which is linked with improved processing in the pruned cortical regions. So, as pruning of the grey matter occurs in childhood and adolescence, broad areas of the cortex, including the left SPL, leaves more mature brains smaller.  Considering that pruning is a process of maturation, then smaller brains or grey matter density volumes could lead the left SPL to be more efficient in attentional control. 

Mother nature continues to be a formidable adversary!!