17860
An MEG Study of Motor-Related Beta Oscillations during Motor Imitation in Autism
As early as 20 months of age, children with autism exhibit a robust deficit in imitating the actions of other people. Diverse explanations for imitative difficulties in ASD have been proposed, including motor and sensory perception control deficits. Indeed, studies have found impairments in many aspects of motor function, including coordination, gait, motor imitation and preparation in both adults and children with autism. Moreover, abnormalities in motor-induced cortical rhythms have been reported in ASD adults while performing motor imitation tasks. To date, however, children with ASD haven’t been investigated.
Objectives:
To compare motor-related brain oscillations in control participants to patients with autism during a motor imitation task.
Methods:
Neuromagnetic activity was recorded in 11 children with ASD (including 4 Asperger’s syndrome) and 12 typically developing control children, during right hand imitation of finger-lifting movements from an animated right hand projected on a screen facing the subject. Index and little fingers were lifted in response to animations of each finger in random order. Oscillatory changes within the beta frequency band (15-30 Hz) were calculated during and following movement, relative to the baseline activity. Decreased beta power (ERD, event-related desynchronization) was observed prior to and during the movement and imaged using a -500 to 500 msec time window (with time 0 being the onset of the movement). Following the movement, an increase in beta-band power (PMBR, post-movement beta rebound) was imaged using a 700 to 2000 ms time window. PMBR and ERD of each group were compared at the sensor level in each hemisphere. Eight channels in the vicinity of the motor cortex were selected per hemisphere. Results were averaged per hemisphere and subjected to group statistical analysis using a 2 samples t-test.
Results:
As expected for a right hand movement, we found relevant motor-associated beta oscillations in both hemispheres, contralateral and ispilateral to the movement, during imitation of both fingers. In the left hemisphere (contralateral), ERD was significantly more robust in the autism group compared to the controls for both index (p=0.01) and little (p=0.03) movements. In contrast, PMBR might have been reduced in ASD subjects, although it did not reach statistical significance, during imitation of index (p=0.06) and little (p=0.07) lifting movements. In the right hemisphere (ipsilateral), no group difference was found in the beta-band independently of the movement performed.
Conclusions:
These results provide some physiological evidence of distinct brain activity associated with imitation of hand movements in children with autism. ERD reflects movement preparation, and it is possible that the greater ERD in autism was due to increased motor and/or imitation planning difficulty. PMBR is generally associated with motor deactivation or inhibition and has been correlated with GABA concentration within the brain. Our trend towards a reduced PMBR in autism is interesting in light of a recent study showing decreased GABA level in the motor cortex in ASD.