Oberman, L.M., Hubbard, E.M., McCleery, J.P., Altschuler, E.L., Ramachandran, V.S., & Pineda, J.A. (2005).
EEG evidence for mirror neuron dysfunction in autism spectrum disorders
Cognitive Brain Research 24, 190-198
Review of the evidence for mirror units in humans
Can’t be studied ( KRO therefore identified and substantiated) directly in humans
P191 ‘the existence of an analogous system ( KRO to that of monkeys) in the homologous brain region ( Broca’s area, Brodmann’s area 44) has been supported by indirect population-level measures
- Ref 17 (1995)Fadiga et al using TMS ‘motor evoked potentials in response to TMS over motor cortex were enhanced when the subject observed another individual performing an action relative to when the subject detected the dimming of a light.
- Ref 39 (1995)Parsons et al used PET to map the brain areas that were active during observation of biological movement. Frontal, parietal and cerebellar regions, including the inferior premotor cortex ( Brodmann’s area 44 – Kro thought to be equivalent to F5 of monkeys) were found to be active during actual movement, imagined movement and observed movement.
- Ref 29 Iacoboni et al (1999)using FMRI found increased blood flow in Brodmann’s area 44 during both observed and performed actions. Ref 10,36 (more recent refs) seem to confirm that these areas are implicated
Also ‘Several recent studies have uncovered activations with similar properties in the parietal cortex ( 10.39) as well as superior temporal sulcus (11,40). These results suggest that the frontal mirror unit system may be one part of a broader action observation/execution network (18.38).’
Monitoring mu rhythm as an indirect method of investigating mirror units in humans
P191 claim ‘ at rest sensorimotor neurons spontaneously fire in synchrony leading to large amplitude EEG oscillations in the 8-13 frequency band. When subjects perform an action, these units fire asynchronously, thereby decreasing the power of the mu-band EEG oscillations ( 41,48). Because the motor properties of the mirror neurons are indistinguishable from those of neighbouring premotor, motor or sensorimotor neurons, mu wave suppression during self-performed actions is likely to be the a
result of activation of several neuronal systems …….During observed hand movement , however, the mirror neuron system is the only network that has been identified to be active in this area of the cortex. ( KRO assumption, speculation?)
Mu power recorded from electrodes on scalp locations C3, Cz & C4 is reduced in normal adults by self initiated movement and observed movements (5,14,26,42)
Rationale for this research
Calls on evidence that ‘human mirror neuron system has been implicated in a variety of higher-level cognitive processes …imitation, language, theory of mind and empathy (refs 54 & 46) all of which are characteristic of ASD.
P191 ‘ once another individuals actions are represented and understood in terms of one’s own actions, it is possible to predict the mental state of the observed individual, leading to theory of mind deficits’ ‘ Empathy may critically depend on one’s ability to understand the observed facial expressions in terms of one’s own motor representations’ ( KRO but first time that the paper mentions facial expression as part of imitative movement)
Research methodogy
ASDs & controls NOTE age range 6-47 did correlation against age , reported as no correlation rather than reporting individual r values ( calculated r across three conditions and three targeted electrode placements and two participant groups ie across nine values of r for each participant group). Also don’t know the distribution of ages in the two groups. All male.
4 conditions – (i) moving own hand, (ii) watching a video of a moving hand, (iii) watching a video of two bouncing balls ( non –biological motion) (iv) watching white visual noise (baseline). (KRO absence of noise and other wild features)
Counting task , number of times the movement stopped, to control for attentional aspects.
EEG
Mastoid refes. F3, Fz,F4,C3,Cz,C4,P3,Pz,P4,T5,T6,O1,& O2 using a cap. But used recordings from C3,Cz & C4 claiming that p194 ‘although data were obtained from electrodes across the scalp, mu rhythmn is defined as oscillations measured over sensorimotor cortex thus only data from C3, Cz and C4 presented’
Data collected for 170 seconds per condition at a sampling rate of 500 HZ. Recognised that recodings at C3,Cz & C4 might be affected by changes in awareness ( KRO therefore alpha) and therefore first 10 s of each block were removed to eliminate the possibility of attentional transients. Also claims that since eyes were open throughout then any alpha rhythm would be at attenuated. EOG used to monitor artefact (eye & head only) and used to remove artefact from records. Integrated power measurement in 8-13 Hz range. P193 ‘data were segmented into epochs of 2 seconds beginning at the start of the segment, FFT were performed on the epoched data (1024 points). A cosine window was used to control for artefacts resulting from data splicing’
2 measures of mu suppression
(1i) power ratio observed hand movement /baseline
(1ii) power ratio self hand movement/baseline
(2i) power ratio observed hand movement /ball movement
(2ii) power ratio self hand movement/ball movement
1 controls for individual differences
2 controls for counting
Based comparison between two groups on log ratios with less than zero indicating suppression and more than zero indicating enhancement.
Results
Based on recordings at C3, CZ, C4 p195 ‘ there was a lack of suppression in the ASD group during the observed hand movement condition suggestive of a dysfunction in the mirror neuron system’ ‘ Furthermore the lack of suppression during the observation conditions in the ASD group is contrasted with significant suppression to their own movement., which is indicative of normal functioning of other sensorimotor systems involved in self-performed actions. P194 ‘No other electrodes showed a consistent pattern of suppression in the frequency band of interest’ (KRO but why was this data not presented as it would be useful to see.)
Discussion
Was the counting task a confounding factor? ( differential effect on the ASD subjects) Didn’t have to count in the baseline condition but did in the bat and ball so that explanation seems unlikely.
Supporting evidence from other work
P195 based on ref 37 ‘ averaging MEG to the presentations of a woman performing orofacial gestures and instructed to imitate. Activations in inferior temporal lobe and primary motor cortex were weaker and had greater latency in the AS group when compared with the control group’
Authors recognise the potential for a low level explanation ‘ p196 ‘ the impaired visual processing of biological motion. This would result in reduced activation in visual areas thought to be involved in biological motion perception’
Differences could be due to inhibitory influences from other brain processes and therefore brain regions.
Further work: looking at metaphorical statements of movement egg rap the idea, reach for the stars.
