RL'iiahilitacija IL·tnil-. VII. 11111I ../ / :!IHJSJ 
SNIFF/NG-RELATED CORTICAL MOTOR 
POTENTIALS IN ALS - A PRELIMINARYI 
REPORT 
M. Korošec, l. Zidar, D. Jeran, 8. Koritnik, J. Zidar
Institute of Clinical Neurophysiology, University Medical Centre Ljubljana, Ljubljana, Slovenia
BACKGROUND 
Respiratory insufficiency is by far the most frequent cause of 
death in amyotrophic laterni sclerosis (ALS). Neural control 
of breathing depends on a central drive to the respiratory 
muscles. Affection of the latter, which is in clinical set­
ting most difficult to assess in isolation, may contribute to 
respiratory deficiency in ALS. A possible way to study the 
central mechanisms for the control of voluntary breathing is 
through different respiratory manoeuvres, e.g. sniffing and 
coughing. Movement-related cortical potentials (MRCPs) 
mainly reflect functioning of the supplementary, premotor 
and primary motor areas that are involved in sniffing as 
well. 
OBJECTIVE 
To determine whether MRCPs evoked by sniffing (sniffing­
related cortical potentials - SRCPs) can serve as a use­
ful marker of cortical respiratory drive dysfunction. We 
hypothesised that SRCP amplitude is reduced in ALS due 
to neuronal loss. We were also interested if sizes of SRCPs 
correlate with overall and specific respiratory functional 
scores and results of pulmonary function tests. 
METHODS 
Eight patients (48-75 years; 4 with definite and 4 with 
probable ALS according to El-Escorial criteria) and 10 
healthy control subjects (21-26 years) were studied. None 
of the patients had symptoms or clinical signs of respiratory 
insufficiency. Both groups performed self-pacecl sniffing 
manoeuvre every 5-10 seconds, patients with 20% and 
controls with 30% of maximal sniff nasal inspiratory pres-
lil 
sure. Onset of sniff nasal inspiratory pressure was used for 
back-averaging of electroencephalogram ( 10- 10 system, 32 
electrodes). MRCPs on right index finger flexion was used 
as a comparison. The maximum amplitudes of SRCPs and 
MRCPs as well as amplitudes at 500 ms and 100 ms before 
and at the time of sniff/finger flexion (O ms) were measured. 
Grand average was calculated for each task. A three-way 
mixed ANOVA and Pearson 's correlation coefficient were 
used for statistical analysis. 
RESULTS 
On grand average, MRCPs and SRCPs of ALS patients were 
larger compared to controls, but the differences wcre not 
statistically significant. No correlation was found between 
sizes of individual SRCP components' and age, overall and 
specific respiratory and upper limb subdiv isions of Norris 
and ALS FSRr scores, and results of pulmonary function 
tests. 
CONCLUSIONS 
The findings are in contrast with our hypothesis. A tendency 
toward increased SRCPs and MRCPs may suggest that 
degeneration of upper and lower motor neurons in ALS is 
parallelecl by processes that compensate for such loss. Plastic 
changes possibly involve recruitment into the response of 
additional generator cells within and adjacent to the motor 
cortical areas that are not called upon in physiologic cir­
cumstances (e.g. by reduction of neuronal celi inhibition). 
The drawbacks of our study are small number of patients 
that do not include those with clinically overt respiratory 
dysfunction, large interindividual variability ofSRCPs, and 
non-matched control group.