Brain Areas Critical To Human Time Sense Identified
Now researchers at the Medical College of Wisconsin in Milwaukee and Veterans
Affairs Medical Center in Albuquerque have identified areas in the brain
responsible for perceiving the passage of time in order to carry out critical
everyday functions, more details at:
unisci.com
Timing is everything. It comes into play when making split second decisions,
such as knowing when to stop at a red light, catch a ball or modulate rhythm
when playing the piano.
Now researchers at the Medical College of Wisconsin in Milwaukee and Veterans
Affairs Medical Center in Albuquerque have identified areas in the brain
responsible for perceiving the passage of time in order to carry out critical
everyday functions.
Their study is the first to demonstrate that the basal ganglia located deep
within the base of the brain, and the parietal lobe located on the surface of
the right side of the brain, are critical areas for this time-keeping system.
Their results are published in the current issue of Nature Neuroscience.
Importantly, the study calls into question a long-standing and widely held
belief in the scientific community that the cerebellum is the critical
structure involved in time perception.
"We are excited that our findings can also have application to better
understand some neurological disorders," says Stephen M. Rao, Ph.D., professor
of neurology at the Medical College and principal investigator. "By
identifying
the area in the brain responsible for governing our sense of time, scientists
can now study defective time perception, which has been observed in patients
with Parkinson's disease and Attention-Deficit/Hyperactivity Disorder (ADHD),
two maladies commonly thought to have abnormal function within the basal
ganglia."
Making accurate decisions regarding the duration of brief intervals of time
from 300 milliseconds to 10 seconds is critical to most aspects of human
behavior. Contemporary theories of short interval timing assume the existence
of a timekeeper system within the brain, yet identifying these brain systems
has been elusive and controversial.
Using a novel functional magnetic resonance imaging (fMRI) technique that
tracks second-by-second changes in brain activity, investigators identified
regions within the brain that are critical for this timekeeping system.
Seventeen healthy, young men and women volunteers were imaged while being
asked
to perceive the duration of time between the presentations of two consecutive
tones. One second later, two more tones were presented and subjects were asked
to make a judgment as to whether the duration between the tones was shorter or
longer than the first two tones.
To make sure that the brain systems associated with time perception were
clearly identified, two control tasks were given which involved listening to
tones or estimating their pitch, but not making judgments about their
duration.
Using this fast imaging technique, the investigators were able to isolate only
those areas of the brain activated during presentation of the first two
tones -- when subjects are only perceiving and attending to time. Their
results
conclusively demonstrated that timekeeping functions are governed by the basal
ganglia and the right parietal cortex.
Investigators have long suspected, based on indirect evidence, that the basal
ganglia might be involved in time perception. The basal ganglia have nerve
cells that primarily contain the neurotransmitter, dopamine.
Patients with Parkinson's disease have an abnormal reduction in dopamine
within
the basal ganglia and commonly experience problems with time perception. These
difficulties partially improve when patients are administered a drug that
increases dopamine levels in the brain.
Defective time perception has also been observed in patients with Huntington's
disease and Attention-Deficit/Hyperactivity Disorder (ADHD), two disorders
commonly thought to have abnormal function within the basal ganglia. Animal
studies have also demonstrated the importance of dopamine in timekeeping.
Medical College researchers at Froedtert Hospital, a major teaching affiliate
of the Medical College, are currently using this new neuroimaging procedure to
better understand how the brain enables dopamine replacement drugs and
methylphenidate (Ritalin) to normalize time perception in individuals with
Parkinson's disease and ADHD, respectively.
An additional study, in collaboration with investigators at the University of
Iowa, will examine time perception in the early stages of Huntington's
disease,
prior to the development of the characteristic movement disorder.
The critical role of the parietal lobes in timekeeping was first suggested by
coauthor Deborah L. Harrington, Ph.D., research scientist, Veterans Affairs
Medical Center and associate research professor of neurology and psychology,
University of New Mexico, Albuquerque, NM. She and her colleagues reported
that
stroke patients with damage to the parietal cortex on the right but not the
left side of the brain experienced impaired time perception.
Patients for the study have been drawn from Froedtert Hospital and the VA
Medical Center in Milwaukee. Additionally, the researchers are studying adult
ADHD patients who have been seen since childhood at the Medical College.
Coauthor of the study with Drs. Rao and Harrington is Andrew R. Mayer, M.S.,
graduate student, department of neurology, Medical College of Wisconsin.
The study was supported by grants from the National Institute of Mental Health
and the W.M. Keck Foundation to the Medical College, and the Department of
Veterans Affairs and National Foundation for Functional Brain Imaging to the
Veterans Affairs Medical Center, Albuquerque. - By Toranj Marphetia