Biology subjects

Jerjian, S. J.

Publications and source records attributed to Jerjian, S. J..

3 recordsLinked to original sources

bioRxiv2020

Top-down contextual requirement to suppress self-movement influences grasp-specific modulation of corticospinal excitability during action observation

Action observation modulates corticospinal excitability (CSE) measured via transcranial magnetic stimulation (TMS) in humans, which presumably exposes the effect of mirror neuron activation on corticospinal pathways. These responses can consist of both facilitation and suppression, and the balance of these two may restrict the outflow of activity into movement. Evidence also suggests that task context can considerably influence CSE changes during action observation. Here, we assessed whether embedding action observation within a Go-NoGo paradigm, emphasizing movement withholding on observation and NoGo trials, influenced CSE modulation. Fourteen healthy subjects received single pulse TMS over left primary motor cortex (M1) during a baseline period, grasp observation onset, or after a NoGo cue, while performing, observing, or withholding two distinct reach-to-grasp actions. We assessed modulation of motor evoked potentials (MEPs) in three intrinsic hand muscles, which were recruited in a grasp-specific manner during action execution. CSE modulation was limited, and predominantly suppressive in nature during grasp observation. Seven subjects performed the same task without the NoGo condition ("Go-only" block) immediately before the "Go&NoGo" block. We found evidence for grasp-specific modulation of CSE, which matched the recruitment pattern of the muscles during action execution. Within these subjects, modulation was attenuated when the NoGo condition was introduced, but was still distinct from modulation in the first group. These results suggest that bottom-up grasp-specific modulation of MEPs during action observation is attenuated by the top-down contextual requirement to suppress self-movement, and facilitation and suppression effects are determined by the balance between these two processes. SIGNIFICANCE STATEMENTAction observation can activate specific pathways in the motor system of the observer, which are also used to perform the same action. This motor resonance, measured via changes in corticospinal excitability using transcranial magnetic stimulation, is susceptible to task context. In this study, we show that observing grasping actions results in grasp-specific changes in excitability, consistent with mirror neuron activation, but this effect is masked when observation is interleaved within a Go-NoGo paradigm, which emphasises suppression of ones own movement. Top-down task requirements to withhold movement within and across trials, which are present in most action observation studies, likely influence the extent of motor resonance, urging caution in the design and interpretation of results in TMS action observation experiments.

neuroscience↗

bioRxiv2019

Movement initiation and grasp representation in premotor and primary motor cortex mirror neurons

Pyramidal tract neurons (PTNs) within macaque rostral ventral premotor cortex (F5) and primary motor cortex (M1) provide direct input to spinal circuitry and are critical for skilled movement control, but surprisingly, can also be active during passive action observation. We recorded from single neurons, including identified PTNs in the hand and arm area of primary motor cortex (M1) (n=189), and in premotor area F5 (n=115) of two adult male macaques, while they executed, observed, or simply withheld (NoGo) reach-to-grasp and hold actions. We found that F5 maintains a more sustained, similar representation of grasping actions during both execution and observation. In contrast, although some M1 neurons mirrored during the grasp and hold, M1 population activity during observation contained signatures of a withholding state. This suggests that M1 and its output may dissociates signals required for the initiation of movement from those associated with the representation of grasp in order to flexibly guide behaviour. Significance StatementVentral premotor cortex (area F5) maintains a similar representation of grasping actions during both execution and observation. Primary motor cortex and its outputs dissociate between movement and non-movement states.

bioinformatics↗

bioRxiv2019

Time-dependent modulation of spinal excitability during action observation in the macaque monkey

Neurons in the primate motor cortex, including identified pyramidal tract neurons projecting to the spinal cord, respond to the observation of others actions, yet this does not cause movement in the observer. Here, we investigated changes in spinal excitability during action observation by monitoring short latency electromyographic responses produced by single shocks delivered directly to the pyramidal tract. Responses in hand and digit muscles were recorded from two adult rhesus macaques while they performed, observed or withheld reach-to-grasp and hold actions. We found modest grasp-specific facilitation of hand muscle responses during hand shaping for grasp, which persisted when the grasp was predictable but obscured from the monkeys vision. We also found evidence of a more general inhibition before observed movement onset, and the size of this inhibition effect was comparable to the inhibition after an explicit NoGo signal. These results confirm that the spinal circuitry controlling hand muscles is modulated during action observation, and this may be driven by internal representations of actions. The relatively modest changes in spinal excitability during observation suggest net corticospinal outflow exerts only minor, sub-threshold changes on hand motoneuron pools, thereby preventing any overflow of mirror activity into overt movement.

animal behavior and cognition↗