Screen Position Preference Offers a New Direction for Action Observation Research: Preliminary Findings Using TMS

Motor imagery drives the effects of combined action observation and motor imagery on corticospinal excitability for coordinative lower-limb actions

Combined action observation and motor imagery (AOMI) facilitates corticospinal excitability (CSE) and may potentially induce plastic-like changes in the brain in a similar manner to physical practice. This study used transcranial magnetic stimulation (TMS) to explore changes in CSE for AOMI of coordinative lower-limb actions. Twenty-four healthy adults completed two baseline (BLH, BLNH) and three AOMI conditions, where they observed a knee extension while simultaneously imagining the same action (AOMICONG), plantarflexion (AOMICOOR-FUNC), or dorsiflexion (AOMICOOR-MOVE). Motor evoked potential (MEP) amplitudes were recorded as a marker of CSE for all conditions from two knee extensor, one dorsi flexor, and two plantar flexor muscles following TMS to the right leg representation of the left primary motor cortex. A main effect for experimental condition was reported for all three muscle groups. MEP amplitudes were significantly greater in the AOMICONG condition compared to the BLNH condition (p = .04) for the knee extensors, AOMICOOR-FUNC condition compared to the BLH condition (p = .03) for the plantar flexors, and AOMICOOR-MOVE condition compared to the two baseline conditions for the dorsi flexors (ps ≤ .01). The study findings support the notion that changes in CSE are driven by the imagined actions during coordinative AOMI.

Using Action-congruent Language Facilitates the Motor Response during Action Observation: A Combined Transcranial Magnetic Stimulation and Eye-tracking Study

There is evidence that action observation (AO) and the processing of action-related words are associated with increased activity in cortical motor regions. Research has examined the effects of AO and action verb processing on activity in the motor system independently. The aim of this experiment was to investigate, for the first time, the modulation of corticospinal excitability and visual attention during the concurrent processing of action verbs and AO stimuli. Twenty participants took part in an integrated transcranial magnetic stimulation and eye-tracking protocol. Single-pulse transcranial magnetic stimulation was delivered to the hand representation of the left motor cortex during (i) observation of a static hand, (ii) AO of a hand squeezing a sponge, (iii) AO of the same action with an audio recording of the word "squeeze," and (iv) AO of the same action with an audio recording of the word "green". Motor evoked potentials were recorded from the abductor pollicis brevis and abductor digiti minimi muscles of the right hand. Eye gaze was recorded throughout the four conditions as a proxy for visual attention. Interviews were conducted to discuss participants' preferences and imagery use for each condition. The AO and action verb condition resulted in significantly increased motor evoked potential amplitudes in the abductor pollicis brevis muscle; participants also made significantly more fixations on the sponge and reported wanting to move their hand more in the action verb condition. The inclusion of auditory action verbs, alongside AO stimuli, in movement simulation interventions could have implications for the delivery of AO interventions for motor (re)learning.

Eye Gaze Markers Indicate Visual Attention to Threatening Images in Individuals with Chronic Back Pain

Research into attentional biases and threatening, pain-related information has primarily been investigated using reaction time as the dependent variable. This study aimed to extend previous research to provide a more in depth investigation of chronic back pain and individuals’ attention to emotional stimuli by recording eye movement behavior. Individuals with chronic back pain (n = 18) were recruited from a back rehabilitation program and age and sex matched against 17 non-symptomatic controls. Participants’ eye movements were recorded whilst they completed a dot probe task, which included back pain specific threatening images and neutral images. There were no significant differences between chronic pain and control participants in attentional biases recorded using reaction time from the dot probe task. Chronic pain participants, however, demonstrated a significantly higher percentage of fixations, larger pupil diameter, a longer average fixation duration and faster first fixation to threatening compared to neutral images. They also had a significantly longer average fixation duration and larger pupil diameter to threatening images compared to control participants. The findings of this study suggest eye gaze metrics may provide a more sensitive measure of attentional biases in chronic pain populations. These findings may have important therapeutic implications for the patient and therapist.

Observation of an action with a congruent contextual background facilitates corticospinal excitability: A combined TMS and eye-tracking experiment

Action observation produces activity in similar regions of the brain to those involved in action execution and can offer an effective intervention for motor (re)learning, although optimal viewing conditions for such interventions remain to be established. In this experiment, single-pulse transcranial magnetic stimulation (TMS) and eye-tracking were used simultaneously to investigate the effect of manipulating background context on both corticospinal excitability and visual attention during action observation. Twenty-four participants observed four different videos: (i) a static hand holding a sponge (control condition); and an index finger-thumb pinch of a sponge against (ii) a plain black background; (iii) a background containing objects that were incongruent with the observed action; and (iv) a background containing objects that were congruent with the observed action. TMS was delivered to the hand representation of the left primary motor cortex, and motor evoked potentials were recorded from the first dorsal interosseous and abductor digiti minimi muscles of the right hand. Eye movements were recorded throughout the experiment. Results indicated that corticospinal excitability was facilitated during the congruent context condition compared to both the static hand and plain black background conditions. In addition, the number of fixations and percentage of time participants spent fixating on the background scene were significantly greater during the incongruent and congruent conditions compared to the static hand and plain black background conditions. These results indicate that the provision of additional visual information that is congruent with the observed movement contributes to a facilitation of corticospinal excitability by providing the observer with information regarding the goal and intention of the observed action. Providing congruent contextual information may enhance the efficacy of action observation interventions for motor (re)learning.