Somatosensory startle reflex (
SSSR) was recently studied in healthy subjects. Following corticospinal tract lesions caused by stroke or spinal cord injury (SCI), auditory startle reflex (ASR) has been reported to enhance due to reorganization of circuits rostral and caudal to the lesion. To further understand changes in SSSR and ASR, we investigated both responses in patients with spinal cord injury (SCI) and stroke.
Methods
We examined characteristics of ASR and SSSR in 14 SCI and 40 stroke patients (16 brainstem and 24 cerebral hemispheric infarctions) and 39 age and gender matched healthy subjects. ASR was obtained after eight auditory stimuli and SSSR was elicited after median nerve stimulation at the wrist. Surface electromyographic recordings were obtained from orbicularis oculi (O.oc), sternocleidomastoid (SCM), biceps brachii (BB) and abductor pollicis brevis (APB) muscles.
Results
Total ASR probabilities at distal muscles were significantly higher in patients with SCI and in stroke patients especially with brainstem infarctions. Similarly SSSR rates were increased in both patient groups compared to controls (for APB p < 0.05). SSR latency of O.oc in SCI patients were similar to controls whereas it was markedly prolonged in stroke patients (p < 0.05).
Conclusions
In conclusion, we have found that SSR and ASR were enhanced in stroke and SCI and this enhancement was more prominent in distal muscles. Secondly, the properties of ASr and SSSR differed according to the lesion site.
