Explicit and implicit motor simulations are impaired in individuals with aphantasia

Abstract

Individuals with aphantasia report having difficulties or an inability to generate visual images of objects or events. So far, there is no evidence showing that this condition also impacts the motor system and the generation of motor simulations. We probed the neurophysiological marker of aphantasia during explicit and implicit forms of motor simulation, i.e., motor imagery and action observation, respectively. We tested a group of individuals without any reported imagery deficits (phantasics) as well as a group of individuals self-reporting the inability to form mental images (aphantasics). We instructed the participants to explicitly imagine a maximal pinch movement in the visual and kinesthetic modalities and to observe a video showing a pinch movement. By means of transcranial magnetic stimulation, we triggered motor-evoked potentials (MEP) in the target right index finger. As expected, MEP amplitude, a marker of corticospinal excitability, increased for phantasics during kinaesthetic motor imagery and action observation relative to rest but not during visual motor imagery. Interestingly, MEP amplitude did not increase in either form of motor simulation for the group of aphantasics. This result provides neurophysiological evidence that individuals living with aphantasia have a real deficit in activating the motor system during motor simulations.

Engaging distributed cortical and cerebellar networks through motor execution, observation, and imagery

“…While the questions of mental imagery in animals currently appears largely intractable to convincing empirical validation, a phenomenon in humans referred to as aphantasia , i.e., the inability to engage in mental imagery ( Dance et al, 2022 ), provides an interesting opportunity to discover more about how mental imagery contributes to our motor and perceptual processing on the neurophysiological level. This field is still in its infancy, but some early studies suggest that motor simulations may indeed be impaired in individuals with aphantasia ( Dupont et al, 2022 ), who also present with measurable alterations in behavioral and neural signatures during mental imagery ( Milton et al, 2021 ; Dupont et al, 2022 ).…”

On the characteristics of aphantasia, hyperphantasia and sensory imagery in a multi-cultural sample

“…Recent neuroimaging (Dupont et al, 2022) and pupillary response (Kay et al, 2022) studies further support this interpretation. Dupont et al (2022) demonstrated that while motor imagery and observation evoked similar brain activity in controls, individuals with aphantasia exhibited an opposite response, suggesting an absence of mental simulation. Kay et al (2022) found no pupillary dilation in aphantasia during visual imagery tasks, unlike controls, further corroborating the lack of imagery in aphantasia.…”

No increase in corticospinal excitability during motor simulation provides a platform to explore the neurophysiology of aphantasia

“…Dupont et al . 1 report the well-established effect that corticospinal excitability is facilitated by kinaesthetic imagery and action observation 3 in participants with typical imagery generation abilities. In contrast, however, these facilitation effects were not found in the participants reporting aphantasia, where corticospinal excitability was not facilitated by either the explicit (kinaesthetic imagery) or implicit (action observation) simulation of movement.…”

“…The study by Dupont et al . 1 published in Brain Communications used single-pulse transcranial magnetic stimulation (TMS) to measure corticospinal excitability during visual imagery, kinaesthetic imagery and action observation of a pinch movement. Participants self-reported either typical imagery abilities or aphantasia (reduced or absent imagery abilities).…”

“…Dupont et al .’s 1 team has an established profile in TMS research and motor imagery processes 3 and used accepted and rigorous TMS methods to conduct the study. Appropriate procedures were used to determine the optimal scalp position and resting motor threshold, to ensure consistent TMS coil placement throughout the study, and to confirm no significant differences in resting pre-stimulation electromyography activity that could potentially skew the data.…”