Document Detail

Effects of a photic input on the human cortico-motoneuron connection.
MedLine Citation:
PMID:  11068233     Owner:  NLM     Status:  MEDLINE    
OBJECTIVES: Disease manifestations such as photic cortical reflex myoclonus or myoclonus due to intermittent light stimulation rely on a pathologic interaction between non-structured visual inputs and the corticospinal system. We wanted to assess the normal interaction, if any, between a prior photic input and the output of the cortico-motoneuron connection. METHODS: In 9 consenting healthy subjects we quantified the changes exerted by a sudden, unexpected bright light flash on (i) the motor potentials (MEPs) evoked in the right first dorsal interosseous muscle (FDI) by transcranial magnetic or electrical stimulation (TMS/TES) of the primary motor cortex, (ii) the FDI F-waves and (iii) the soleus H-wave. Separately, we measured the simple reaction times to the flash itself. All determinations were repeated twice with an interval of 2-24 months. RESULTS: When the flash preceded TMS by 55-70 ms, the MEP size was reduced, while at interstimulus intervals (ISIs) of 90-130 ms it was enlarged. Statistical significance (P<0.05) emerged at ISIs of 55, 70, 100, 105 and 120 ms. Conversely, the MEP latency was prolonged at ISIs of 55-70 ms and shortened at ISIs of 90-130 ms (P<0.05 at ISIs of 55, 110 and 130 ms). Electrical MEPs were enhanced at an ISI of 120 ms. The F-wave size showed a non-significant trend of enhancement at ISIs of 90-130 ms. The soleus H-wave showed significant enlargement at ISIs of 90-130 ms (P<0.05 at ISIs of 100 and 105 ms). The minimum reaction time was on average 120 ms. CONCLUSIONS: An unexpected photic input, to which no reaction is planned, can cause an early inhibition of the responses to TMS. We think its origin lies within the primary motor cortex, since it is not associated with changes in spinal excitability or electrical MEPs. A later facilitation persists using TES and has a temporal relationship with an enlargement of the soleus H-wave. Thus, it likely results from activation of descending (possibly reticulospinal) fibers that excite the spinal motor nucleus.
R Cantello; C Civardi; A Cavalli; C Varrasi; R Vicentini
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology     Volume:  111     ISSN:  1388-2457     ISO Abbreviation:  Clin Neurophysiol     Publication Date:  2000 Nov 
Date Detail:
Created Date:  2000-12-15     Completed Date:  2001-01-11     Revised Date:  2008-09-10    
Medline Journal Info:
Nlm Unique ID:  100883319     Medline TA:  Clin Neurophysiol     Country:  NETHERLANDS    
Other Details:
Languages:  eng     Pagination:  1981-9     Citation Subset:  IM    
Department of Medical Sciences, Section of Neurology, Università del Piemonte Orientale "Amedeo Avogadro", Novara, Italy.
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MeSH Terms
Brain / physiology*
Electric Stimulation
Evoked Potentials, Motor / physiology*
Muscles / physiology
Photic Stimulation*
Reaction Time / physiology
Reference Values

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