Development of corticospinal motor excitability and cortical silent period from mid-childhood to adulthood - a navigated TMS study.
OBJECTIVES
We characterized the maturation of the excitability of the motor cortex and corticospinal tract from childhood to adulthood using electric field (EF) navigated TMS and correlated the results with manual dexterity.


METHODS
Both hemispheres of healthy right-handed children (6-9 years, n=10), preadolescents (10-12 years, n=13), adolescents (14-17 years, n=12) and young adults (22-34 years, n=12) of both genders were examined. The optimal cortical representation site and resting motor threshold (rMT) were determined for the abductor pollicis brevis muscle. Motor-evoked potential (MEP) latencies and amplitudes in relaxed and active states, input-output curves and silent period (SP) durations were determined. Manual dexterity was assessed with the Box and Block Test.


RESULTS
rMT (in terms of maximal stimulator output or EF strength) decreased with age (P<0.001) and stabilized when reaching adolescence. The MEP amplitude (P=0.037) and latency increased (P<0.001) with age. Input-output curves showed age-dependent changes in several parameters. SP duration decreased with age (P<0.001), and demonstrated hemispheric asymmetry in the children (P=0.030). Manual dexterity correlated negatively with rMT (P<0.001).


DISCUSSION
The excitation/inhibition balance develops with age and correlates with manual dexterity. Strong corticospinal inhibition was observed in the children and this was found to decrease with age. Interhemispheric asymmetry was only observed for SP duration in the children. Knowledge of normal development is crucial for the understanding of developmental disabilities and using estimates of effective EF may be advantageous in future pediatric studies.
['Säisänen|Laura|L|', 'Julkunen|Petro|P|', 'Lakka|Timo|T|', 'Lindi|Virpi|V|', 'Könönen|Mervi|M|', 'Määttä|Sara|S|']
D000293:Adolescent D000328:Adult D002648:Child D004558:Electric Stimulation D004576:Electromyography D019054:Evoked Potentials, Motor D005260:Female D006801:Humans D008297:Male D009044:Motor Cortex D018482:Muscle, Skeletal D009433:Neural Inhibition D011712:Pyramidal Tracts D050781:Transcranial Magnetic Stimulation D055815:Young Adult
Development Excitability Silent period Motor cortex Human maturation Transcranial magnetic stimulation