A review of: GILBERT, S., BIRD, G., BRINDLEY, R., FRITH, C., BURGESS, P. (2008). Atypical recruitment of medial prefrontal cortex in autism spectrum disorders: An fMRI study of two executive function tasks. Neuropsychologia DOI: 10.1016/j.neuropsychologia.2008.03.025
Executive functioning is an umbrella term used in clinical neuropsychology and cognitive neurosciences to refer to a series of “higher-order” cognitive processes usually associated with frontal lobe functioning. These include planning, organizing, categorizing, response inhibition, monitoring, multitasking, etc. Research on executive functioning and autism has provided mixed results likely due to differences in the area of executive function measured. In this functional MRI study, the authors used a new test of executive function used to assess for stimulus dependent vs. stimulus independent thoughts. Stimulus dependent refers to cognitive processing (thinking) that is associated with, or dependent on, a specific stimulus that is presented. For example, I may ask you to press the b key when you see a blue square or the r key when you see a red square. For this task the stimulus dependent phase consisted of capital letters presented in alphabetical order. Once a letter was presented, the person had to press one key if the letter contained only straight lines (such as the letter A) and a different key if the letter contained curves (such as the letter B). In the stimulus independent task, the person was presented with one letter and ask to follow the same response pattern (one key if straight lines – another key if curves). However, the second letter presented was random and did not follow the alphabetical order, yet the person was asked to respond based on the next alphabetical letter. For example, assume the first letter was “C”, then the next letter presented was the letter “H” (random) yet the person was asked to respond to the next alphabetical letter starting from the first letter presented (C), thus the next response was based on the characteristics of the letter D, even though the person was seeing the letter H. This task therefore, requires the person to continue to “think” of the characteristics of the letters in alphabetical order, independent of the letters presented (which now are distractors).
In the study the authors examined 15 adults with high functioning autism and 18 typically developing adults that were matched for age (mean 38) and IQ (mean 119). The participants performed the task while undergoing a functional magnetic resonance imaging scan (fMRI). There was no difference in accuracy or response times between the groups. Both groups showed more activation of the lateral frontal and parietal cortex on the more difficult stimulus-independent task. However, the autism group had significantly more activation of specific areas of the medial prefrontal cortex during the easier stimulus dependent condition than the typically developing group (this was interpreted as failure to deactivate these areas). The authors argued that these results suggest an atypical brain organization in HFA with limited deactivation of the rostral prefrontal cortex during easier task compared to typically developing individuals. However, the equivalent performance (both groups did just as well on the task) suggests that the fMRI findings simply reflect different approaches to cognitive performance between the two groups.