Document Detail

Patterned ballistic movements triggered by a startle in healthy humans.
MedLine Citation:
PMID:  10200438     Owner:  NLM     Status:  MEDLINE    
1. The reaction time to a visual stimulus shortens significantly when an unexpected acoustic startle is delivered together with the 'go' signal in healthy human subjects. In this paper we have investigated the physiological mechanisms underlying this effect. If the commands for the startle and the voluntary reaction were superimposed at some level in the CNS, then we would expect to see alterations in the configuration of the voluntary response. Conversely, if the circuit activated by the startling stimulus is somehow involved in the execution of voluntary movements, then reaction time would be sped up but the configuration of the motor programme would be preserved. 2. Fourteen healthy male and female volunteers were instructed to react as fast as possible to a visual 'go' signal by flexing or extending their wrist, or rising onto tiptoe from a standing position. These movements generated consistent and characteristic patterns of EMG activation. In random trials, the 'go' signal was accompanied by a very loud acoustic stimulus. This stimulus was sufficient to produce a startle reflex when given unexpectedly on its own. 3. The startling stimulus almost halved the latency of the voluntary response but did not change the configuration of the EMG pattern in either the arm or the leg. In some subjects the reaction times were shorter than the calculated minimum time for processing of sensory information at the cerebral cortex. Most subjects reported that the very rapid responses were produced by something other than their own will. 4. We conclude that the very short reaction times were not produced by an early startle reflex adding on to a later voluntary response. This would have changed the form of the EMG pattern associated with the voluntary response. Instead, we suggest that such rapid reactions were triggered entirely by activity at subcortical levels, probably involving the startle circuit. 5. The implication is that instructions for voluntary movement can in some circumstances be stored and released from subcortical structures.
J Valls-Solé; J C Rothwell; F Goulart; G Cossu; E Muñoz
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Publication Detail:
Type:  Clinical Trial; Journal Article; Randomized Controlled Trial; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  The Journal of physiology     Volume:  516 ( Pt 3)     ISSN:  0022-3751     ISO Abbreviation:  J. Physiol. (Lond.)     Publication Date:  1999 May 
Date Detail:
Created Date:  1999-07-29     Completed Date:  1999-07-29     Revised Date:  2013-06-11    
Medline Journal Info:
Nlm Unique ID:  0266262     Medline TA:  J Physiol     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  931-8     Citation Subset:  IM    
Unitat d'EMG, Servei de Neurologia, Departament de Medicina, Hospital Clinic, Universitat de Barcelona, Barcelona, Spain.
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MeSH Terms
Acoustic Stimulation
Movement / physiology*
Reaction Time / physiology*
Startle Reaction / physiology*
Wrist / innervation,  physiology

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