The StartReact effect in tasks requiring end-point accuracy

Word Repetition Paired With Startling Stimuli Decreases Aphasia and Apraxia Severity in Severe-to-Moderate Stroke: A Stratified, Single-Blind, Randomized, Phase 1 Clinical Trial

PURPOSE

This prospective, single-blinded, parallel, stratified, randomized clinical trial via telehealth aimed to investigate the impact of Startle Adjuvant Rehabilitation Therapy (START) on aphasia, apraxia of speech (AOS), and quality of life in individuals with chronic stroke. The study hypothesized that START would have a greater effect on AOS-related measures and more severe individuals.

METHOD

Forty-two participants with poststroke aphasia, AOS, or both were randomly assigned to the START or control group. Both groups received 77-dB GET READY and GO cues during a word repetition task for three 1-hr sessions on consecutive days. The START group additionally received 105-dB white noise GO cues during one third of trials. The Western Aphasia Battery-Revised, Apraxia Battery for Adults, Stroke Impact Scale, and Communication Outcomes After Stroke scale were administered at Day 1, Day 5, and 1-month follow-up.

RESULTS

START improved performance on some subtests of the Western Aphasia Battery (Comprehension, Repetition, Reading) and measures of AOS (Diadochokinetic Rate, Increasing Word Length) in individuals with moderate/severe aphasia, whereas moderate/severe controls saw no changes. Individuals with mild aphasia receiving START had improved Reading, whereas mild controls saw improved Comprehension. The START group had increased mood and perceived communication recovery by Day 5, whereas controls saw no changes in quality of life.

CONCLUSIONS

This study is the first to evaluate the impact of training with startling acoustic stimuli on clinical measures of aphasia and AOS. Our findings suggest START can enhance both nontrained speech production and receptive speech tasks in moderate/severe aphasia, possibly by reducing poststroke cortical inhibition. Our findings should be considered carefully, as our limitations include small effect sizes, within-group variability, and low completion rates for quality-of-life assessments and follow-up visits. Future studies should explore a mechanism of action, conduct larger and longer Phase 2 clinical trials, and evaluate long-term retention.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.24093519.

Impact of Startling Acoustic Stimuli on Word Repetition in Individuals With Aphasia and Apraxia of Speech Following Stroke

PURPOSE

The StartReact effect, whereby movements are elicited by loud, startling acoustic stimuli (SAS), allows the evaluation of movements when initiated through involuntary circuitry, before auditory feedback. When StartReact is applied during poststroke upper extremity movements, individuals exhibit increased muscle recruitment, reaction times, and reaching distances. StartReact releases unimpaired speech with similar increases in muscle recruitment and reaction time. However, as poststroke communication disorders have divergent neural circuitry from upper extremity tasks, it is unclear if StartReact will enhance speech poststroke. Our objective is to determine if (a) StartReact is present in individuals with poststroke aphasia and apraxia and (b) SAS exposure enhances speech intelligibility.

METHOD

We remotely delivered startling, 105-dB white noise bursts (SAS) and quiet, non-SAS cues to 15 individuals with poststroke aphasia and apraxia during repetition of six words. We evaluated average word intensity, pitch, pitch trajectories, vowel formants F1 and F2 (first and second formants), phonemic error rate, and percent incidence of each SAS versus non-SAS-elicited phoneme produced under each cue type.

RESULTS

For SAS trials compared to non-SAS, speech intensity increased (∆ + 0.6 dB), speech pitch increased (∆ + 22.7 Hz), and formants (F1 and F2) changed, resulting in a smaller vowel space after SAS. SAS affected pitch trajectories for some, but not all, words. Non-SAS trials had more stops (∆ + 4.7 utterances) while SAS trials had more sustained phonemes (fricatives, glides, affricates, liquids; ∆ + 5.4 utterances). SAS trials had fewer distortion errors but no change in substitution errors or overall error rate compared to non-SAS trials.

CONCLUSIONS

We show that stroke-impaired speech is susceptible to StartReact, evidenced by decreased intelligibility due to altered formants, pitch trajectories, and articulation, including increased incidence of sounds that could not be produced without SAS. Future studies should examine the impact of SAS on voluntary speech intelligibility and clinical measures of aphasia and apraxia.

Movement preparation time determines movement variability

Faster movements are typically more variable-a speed-accuracy trade-off known as Fitts' law. Are movements that are initiated faster also more variable? Neurophysiological work has associated larger neural variability during motor preparation with longer reaction time (RT) and larger movement variability, implying that movement variability decreases with increasing RT. Here, we recorded over 30,000 reaching movements in 11 human participants who moved to visually cued targets. Half of the visual cues were accompanied by a beep to evoke a wide RT range in each participant. Results show that initial reach variability decreases with increasing RT, for voluntarily produced RTs up to ∼300 ms, whereas other kinematic aspects and endpoint accuracy remained unaffected. We conclude that movement preparation time determines initial movement variability. We suggest that the chosen movement preparation time reflects a trade-off between movement initiation and precision.NEW & NOTEWORTHY Fitts' law describes the speed-accuracy trade-off in the execution of human movements. We examined whether there is also a trade-off between movement planning time and initial movement precision. We show that shorter reaction times result in higher initial movement variability. In other words, movement preparation time determines movement variability.

Assessment of trunk flexion in arm reaching tasks with electromyography and smartphone accelerometry in healthy human subjects

Trunk stability is essential to maintain upright posture and support functional movements. In this study, we aimed to characterize the muscle activity and movement patterns of trunk flexion during an arm reaching task in sitting healthy subjects and investigate whether trunk stability is affected by a startling acoustic stimulus (SAS). For these purposes, we calculated the electromyographic (EMG) onset latencies and amplitude parameters in 8 trunk, neck, and shoulder muscles, and the tilt angle and movement features from smartphone accelerometer signals recorded during trunk bending in 33 healthy volunteers. Two-way repeated measures ANOVAs were applied to examine the effects of SAS and target distance (15 cm vs 30 cm). We found that SAS markedly reduced the response time and EMG onset latencies of all muscles, without changing neither movement duration nor muscle recruitment pattern. Longer durations, higher tilt angles, and higher EMG amplitudes were observed at 30 cm compared to 15 cm. The accelerometer signals had a higher frequency content in SAS trials, suggesting reduced movement control. The proposed measures have helped to establish the trunk flexion pattern in arm reaching in healthy subjects, which could be useful for future objective assessment of trunk stability in patients with neurological affections.

Does exposure to startle impact voluntary reaching movements in individuals with severe-to-moderate stroke?

When movements of individuals with stroke (iwS) are elicited by startling acoustic stimulus (SAS), reaching movements are faster, further, and directed away from the body. However, these startle-evoked movements also elicit task-inappropriate flexor activity, raising concerns that chronic exposure to startle might also induce heightened flexor activity during voluntarily elicited movement. The objective of this study is to evaluate the impact of startle exposure on voluntary movements during point-to-point reaching in individuals with moderate and severe stroke. We hypothesize that startle exposure will increase task-inappropriate activity in flexor muscles, which will be associated with worse voluntarily initiated reaching performance (e.g. decreased distance, displacement, and final accuracy). Eleven individuals with moderate-to-severe stroke (UEFM = 8–41/66 and MAS = 0–4/4) performed voluntary point-to-point reaching with 1/3 of trials elicited by an SAS. We used electromyography to measure activity in brachioradialis (BR), biceps (BIC), triceps lateral head (TRI), pectoralis (PEC), anterior deltoid (AD), and posterior deltoid (PD). Conversely to our hypothesis, exposure to startle did not increase abnormal flexion but rather antagonist activity in the elbow flexors and shoulder horizontal adductors decreased, suggesting that abnormal flexor/extensor co-contraction was reduced. This reduction of flexion led to increased reaching distance (18.2% farther), movement onset (8.6% faster), and final accuracy (16.1% more accurate) by the end of the session. This study offers the first evidence that exposure to startle in iwS does not negatively impact voluntary movement; moreover, exposure may improve volitionally activated reaching movements by decreasing abnormal flexion activity.

When reflex reactions oppose voluntary commands: The StartReact effect on eye opening

A startling auditory stimulus (SAS) induces a reflex response involving, among other reactions, a strong contraction of the orbicularis oculi muscle (OOc) and subsequent eye closure. A SAS also induces the StartReact effect, a significant shortening of reaction time in subjects ready for task execution. We examined the obvious conflict appearing when a StartReact paradigm requires participants with eyes closed to open their eyes to look for a visual target. We recorded OOc EMG activity and eyelid movements in healthy volunteers who were instructed to open their eyes at perception of a somatosensory imperative stimulus (IS) and locate the position of a Libet's clock's hand shown on a computer screen at 80 cm distance. In 6 out of 20 trials, we delivered a SAS simultaneously with the IS. The main outcome measures were reaction time at onset of eyelid movement and the time gap (TG) separating subjective assessment of the clock's hand position from real IS issuing. Control experiments included reaction time to eye closing and target location with eyes open to the same IS. Reaction time was significantly faster in SAS than in noSAS trials and slower for eye opening than for eye closing in both conditions. In the eye-opening task, TG was significantly shorter in SAS with respect to noSAS trials, despite the presence of the SAS-related burst in the OOc before EMG cessation. Our results indicate that the StartReact effect speeds up eye opening and location of a target in the visual field despite the startle reaction opposing the task.

Chemistry and Effects of Brainstem Acting Drugs

BACKGROUND

Brain is the most sensitive organ, whereas brainstem is the most important part of Central Nervous System (CNS). It connects the brain and the spinal cord. However, a myriad of drugs and chemicals affects CNS with severe resultant effects on the brainstem.

METHODS

In view of this, a number of literature were assessed for information on the most sensitive part of brain, drugs and chemicals that act on the brainstem and clinical benefit and risk assessment of such drugs and chemicals.

RESULTS

Findings have shown that brainstem regulates heartbeat, respiration and because it connects the brain and spinal cord, all the drugs that act on the spinal cord may overall affect the systems controlled by the spinal cord and brain. The message is sent and received by temporal lobe, occipital lobe, frontal lobe, parietal lobe and cerebellum.

CONCLUSION

Hence, the chemical functional groups of the brainstem and drugs acting on brainstem are complementary, and may produce either stimulation or depression of CNS.

Startle evokes nearly identical movements in multi-jointed, two-dimensional reaching tasks

StartReact is the ability of the startle reflex to involuntarily release a planned movement in the presence of a loud acoustic stimulus resulting in muscle activity patterns and kinematics that are tightly regulated and scaled with the intended action. Previous studies demonstrated startReact's robustness during simple single-joint reaching tasks and found no difference between startReact and voluntary movements for movement kinematics and muscle activation patterns. However, startReact has not been evaluated during multi-joint reaching movements with multiple degrees of freedom. It is unclear if startReact would evoke accurate and precise multi-joint reaching movements in an unrestricted workspace. Furthermore, if tested more rigorously, multi-joint startReact movement kinematics and muscle activation patterns might not be truly equivalent despite showing no difference through traditional ANOVAs. A previous study found multi-joint startReact was possible during unrestricted elbow and shoulder movement when reaching to a forward target. Therefore, we hypothesized that startReact would evoke similar multi-joint reaching movements for movement accuracy and muscle activation patterns when compared to voluntary movements in a multi-directional workspace. Expanding upon the previous study, our study uses a larger workspace and fully evaluates movement kinematics and muscle activations patterns. Results confirmed our hypothesis and found startReact movements were readily evoked in all directions. StartReact responses presented stereotypically earlier muscle activation, but the relative timing of agonist/antagonist firing pairs between startReact and voluntary movements remained similar. Results demonstrate that startReact is robustly present and equivalent in multi-joint reaching tasks and has potential clinical use for evaluating healthy and impaired movement.

StartReact effects in first dorsal interosseous muscle are absent in a pinch task, but present when combined with elbow flexion

Objective

To provide a neurophysiological tool for assessing sensorimotor pathways, which may differ for those involving distal muscles in simple tasks from those involving distal muscles in a kinetic chain task, or proximal muscles in both.

Methods

We compared latencies and magnitudes of motor responses in a reaction time paradigm in a proximal (biceps brachii, BB) and a distal (first dorsal interosseous, FDI) muscle following electrical stimuli used as imperative signal (IS) delivered to the index finger. These stimuli were applied during different motor tasks: simple tasks involving either one muscle, e.g. flexing the elbow for BB (FLEX), or pinching a pen for FDI (PINCH); combined tasks engaging both muscles by pinching and flexing simultaneously (PINCH-FLEX). Stimuli were of varying intensity and occasionally elicited a startle response, and a StartReact effect.

Results

In BB, response latencies decreased gradually and response amplitudes increased progressively with increasing IS intensities for non-startling trials, while for trials containing startle responses, latencies were uniformly shortened and response amplitudes similarly augmented across all IS intensities in both FLEX and PINCH-FLEX. In FDI, response latencies decreased gradually and response amplitudes increased progressively with increasing IS intensities in both PINCH and PINCH-FLEX for non-startling trials, but, unlike in BB for the simple task, in PINCH for trials containing startle responses as well. In PINCH-FLEX, FDI latencies were uniformly shortened and amplitudes similarly increased across all stimulus intensities whenever startle signs were present.

Conclusions

Our results suggest the presence of different sensorimotor pathways supporting a dissociation between simple tasks that involve distal upper limb muscles (FDI in PINCH) from simple tasks involving proximal muscles (BB in FLEX), and combined tasks that engage both muscles (FDI and BB in PINCH-FLEX), all in accordance with differential importance in the control of movements by cortical and subcortical structures.

Significance

Simple assessment tools may provide useful information regarding the differential involvement of sensorimotor pathways in the control of both simple and combined tasks that engage proximal and distal muscles.

Motor preparation in picture naming tasks

In certain circumstances, words can be uttered as an involuntary action. We hypothesize that, once pronunciation of a word is fully prepared it can be triggered as a reflex with no need for cortical processing. We used modified protocols of picture naming tasks, with different levels of cognitive demands, to measure reaction time to word pronunciation (RTWP). In test trials, picture presentation was accompanied by a startling auditory stimulus (SAS). When one and the same picture was repeatedly shown, SAS shortened RTWP by about 30% (StartReact effect), which did not occur when random pictures were shown. If subjects were led to learn which picture was to appear after repeated presentation of three pictures in sequence, they exhibited again the StartReact effect. We conclude that word pronunciation may be fully prepared for execution in absence of cognitive demands. However, the StartReact effect is inhibited during cognitive tasks.

Startle reveals decreased response preparatory activation during a stop-signal task

In a stop-signal task participants are instructed to initiate a movement in response to a go signal, but to inhibit this movement if an infrequent stop signal is presented after the go. Reaction time (RT) in a stop-signal task is typically longer compared with that in a simple RT task, which may be attributed to a reduced readiness to initiate the response caused by the possibility of having to inhibit the response. The purpose of this experiment was to probe the preparatory activation level of the motor response during a stop-signal task using a startling acoustic stimulus (SAS), which has been shown to involuntarily trigger sufficiently prepared responses at a short latency. Participants completed two separate tasks: a simple RT task, followed by a stop-signal RT task. During both tasks, an SAS (120 dB) was pseudorandomly presented concurrently with the go signal. As expected, RT during the simple RT task was significantly shorter than during the stop-signal task. A significant reduction in RT was noted when an SAS was presented during the simple RT task; however, during the stop-signal task, an SAS resulted in either a significant speeding or a moderate delay in RT. Additionally, the subset of SAS trial responses with the shortest RT latencies produced during the stop-signal task were also delayed compared with the short-latency SAS trial responses observed during the simple RT task. Despite evidence that a response was prepared in advance of the go signal during a stop-signal task, it appears that the amount of preparatory activation was reduced compared with that achieved during a simple RT task.