Neural Correlates of Motor-Linked Implicit Learning in Autism Spectrum Disorders

Background:

Motor-linked implicit learning is the learning of a sequence of movements without conscious awareness (e.g., getting faster at typing one's own name as a byproduct of signing emails). Although motor symptoms are frequently reported in persons with autism spectrum disorders (ASD), recent behavioral studies have suggested that motor-linked implicit learning may be intact in ASD (e.g. Barnes, et al., 2008; Müller et al., 2004; Travers et al., 2008). Nevertheless, persons with ASD may recruit different cortical areas while engaging in this type of learning. The serial response task (SRT) is one of the most common measures of motor-linked implicit learning. In neurotypical individuals, the SRT activates the premotor, sensorimotor, primary motor, anterior cingulate, caudate, and medial prefrontal cortices (Destrebecqz et al., 2007). In this study, an SRT experiment was used in an fMRI scanner to investigate the cognitive and neural responses to motor-linked implicit learning in persons with ASD.

Objectives:

The present study sought to examine whether different patterns of fMRI measured brain activation occurred for motor-linked implicit learning in persons with ASD compared to neurotypical controls.

Methods:

Eight high-functioning adolescents and adults with ASD and twelve age and IQ matched controls participated in this study (data collection is ongoing). The data were collected using a Siemens 3T Allegra fMRI scanner. Participants completed an SRT in which they responded with a button press to the picture of an airplane displayed on the screen in one of four possible locations. Unknown to participants, the location of the airplane followed a repeating 12-step sequence of movement. Participants completed 12 alternating blocks of sequenced and non-sequenced trials. There were no breaks or delineations between sequenced and non-sequenced blocks.

Results:

Behavioral results suggest that the participants with ASD demonstrated less motor-linked implicit learning indicated by a smaller reaction time difference between non-sequenced and sequenced blocks in participants with ASD (M = +8 ms) than neurotypical controls (M = +35 ms). Furthermore, the fMRI results suggest that different cortical areas were recruited by participants with ASD during motor-linked implicit learning. Specifically, participants with ASD showed less bilateral sensorimotor (postcentral gyrus) and primary motor (precentral gyrus) activation than neurotypical controls. However, participants with ASD activated more in the left inferior frontal gyrus than neurotypical controls. These results suggest less motor-specific activation in participants with ASD compared to neurotypical controls.

Conclusions:

Behaviorally, motor-linked implicit learning may be less robust in persons with ASD. At the neural level, people with ASD showed atypical brain responses, especially in terms of less sensitivity to the sequenced blocks of trials in the sensorimotor and primary motor cortices and more sensitivity to the sequenced blocks of trials in the inferior frontal gyrus compared to neurotypical controls. This suggests that persons with ASD may be using more frontal-mediated, explicit and effortful learning rather than motor-mediated implicit learning during the SRT.