This study will use repetitive transcranial magnetic stimulation, or rTMS (magnetic
stimulation to the brain), to examine how the brain distinguishes between two signals that
are spaced very closely in time. The ability to tell the difference between sensory signals
is important to understanding sensory input. Understanding how this works may help to
develop new treatments for sensory deficits.
Healthy volunteers 18 years of age and older may be eligible for this study. Participants
undergo the following procedures during three visits to the NIH Clinical Center:
rTMS - all visits (sham rTMS on one visit) :
For TMS, a wire coil is held on the scalp. A brief electrical current passed through the
coil creates a magnetic pulse that stimulates the brain. During the stimulation, the subject
may be asked to tense certain muscles slightly or perform other simple actions.
Theta burst stimulation (TBS) - all visits (sham TBS on one visit):
Same as TMS, but brief pulses of electrical current are passed through the coil. Subjects
undergo intermittent TBS on one visit and continuous TBS on another.
Somatosensory evoked potential (SEP) - all visits:
SEP tests how sensory information travels along the nerves to the spinal cord and brain. A
small metal disk electrode placed on an arm delivers a small electrical shock. Electrodes
placed on the scalp record how the impulse travels over the nerve pathways to the cerebral
cortex of the brain. EEG (see below) records what sensory information the brain is detecting
and processing. Paired-pulse SEP is done before and after TBS.
Temporal discrimination threshold - all visits:
This test investigates the brain's ability to discriminate sensory information. Electrodes
are placed on the subject's wrist. Two electrical pulses are delivered to the nerve at the
wrist at different spaced intervals to determine when the subject feels the two pulses are
fused into one. This test is done before and after TBS.
Electroencephalography (EEG) - all visits:
This test records brain waves (electrical activity of the brain). Electrodes are placed on
the scalp with an electrode cap. The spaces between the electrodes and the scalp are filled
with a gel that conducts electrical activity.
The ability to discriminate successive signals separated by time intervals in the
millisecond-range is an important element in analyzing the temporal characteristics of
sensory input. When two identical stimuli are presented with a sufficient time interval
between them, they are readily perceived as being two separate events. As they are presented
progressively closer together, there comes a point when the two separate stimuli are
perceived as one. However, the neural mechanism of temporal discrimination is unclear.
Therefore, our major objective is to analyze, in detail, the effect of cortical excitability
and inhibition on temporal sensory discrimination in healthy subjects.
We intend to study 25 adult healthy volunteers.
Assuming the cortical circuit in the somatosensory area plays an important role in temporal
discrimination, we plan to investigate the relationship between cortical excitability and
the ability of temporal discrimination. We hypothesize that the extent of cortical
excitability affects the ability to discriminate. Cortical excitability will be modulated by
using repetitive transcranial magnetic stimulation (rTMS). Comparison of cortical
excitability changes will be determined before and after rTMS in the primary somatosensory
cortex (SI). The change in cortical information processing in SI will be studied using
multi-channel electroencephalography (EEG) recording of paired-pulse somatosensory evoked
potentials (SEPs) delivered at rest. Activity assessment in the cortical circuit will be
measured by the recovery curve of the amplitude of paired-pulse SEPs.
The primary outcome measure will be the change in amplitude of the paired-pulse SEP
component (P27) in 5-ms interstimulus interval condition for three types of rTMS. The
secondary outcome will be the amplitude of paired-pulse SEP components during other
interstimulus interval conditions (10 to 200 ms).
- INCLUSION CRITERIA:
- Age 18 years and older
- Absence of dystonia or other neurological conditions
- Concurrent medical, surgical, neurologic or psychiatric condition
- History of neurological disorders
- History of seizure disorder
- Pregnant women
- Presence of pacemaker, implanted medical pump, metal plate or metal object in skull