Exaggerated auditory startle responses in patients with spinal cord injury.
OBJECTIVE
Central nervous system reorganization following spinal cord injury (SCI) may cause functional changes in the motor tracts in patients in whom increased auditory startle responses (ASRs) have been previously reported. We hypothesized that if increased ASRs in patients with incomplete SCI were due to compensatory mechanisms, these changes would be related to severity and/or localization of the lesion.


METHODS
We examined ASR characteristics in 29 SCI patients and 14 age-matched healthy volunteers. Fourteen patients had incomplete and 15 complete SCI; 10 patients had cervical and 19 thoracolumbar SCI. Five auditory stimuli were applied binaurally to subjects in a sitting position, with a 5-min interstimulus interval. Surface electromyographic recordings were obtained from orbicularis oculi (OOc), sternocleidomastoid (SCM), biceps brachii (BB), and tibialis anterior (TA) muscles.


RESULTS
ASR probability was significantly higher and area-under-the-curve was significantly larger in SCM and BB in patients than in controls. ASR latency was significantly shorter in SCM and BB in patients with cervical than in those with thoracolumbar SCI (p < 0.02), but there were no statistically significant differences between complete and incomplete SCI (p > 0.1). Time span since onset correlated significantly with ASR area in OOc, SCM and BB (p < 0.05).


CONCLUSIONS
The capability of the adult central nervous system to reorganize its circuits over time for improved functionality following injury is probably the key to understanding the increased ASRs in patients with SCI. The exaggeration of the startle reflex is potentially important since it may be useful for augmenting voluntary movement in the clinical rehabilitation of patients with SCI.
Kumru
Hatice
H
Dept. of Neurology and Neurorehabilitation, Hospital de Neurorehabilitación Instituto Guttmann, Camí de Can Rutí s/n, 08916 Badalona Barcelona, Spain. hkumru@guttmann.com
Vidal
Joan
J
Kofler
Markus
M
Benito
Jesus
J
Garcia
Alejandro
A
Valls-Solé
Josep
J
D000161:Acoustic Stimulation; D000293:Adolescent; D000328:Adult; D000368:Aged; D001933:Brain Stem / Q000503:physiopathology; D004525:Efferent Pathways / Q000502:physiology; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology; D009431:Neural Conduction / Q000502:physiology; D009460:Neurologic Examination; D009473:Neuronal Plasticity / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D012021:Reflex, Abnormal / Q000502:physiology*; D013216:Reflex, Startle / Q000502:physiology*; D012154:Reticular Formation / Q000503:physiopathology; D013116:Spinal Cord / Q000503:physiopathology*; D013119:Spinal Cord Injuries / Q000503:physiopathology*