MAPS: Magnetic Brain Stimulation

["Nicholas V. Cozzi, Ph.D." <nvcozzi@xxxxxxxxxxxxxxxx>]

A recent topic on this list has been magnetic brain stimulation. 
The April 2, 1999 issue of Science contains the following article
describing exactly this kind of research.  They stimulated the
visual cortex in humans, through the scalp, using magnetic fields. 
Here's the abstract, volume 264, page 167:

The Role of Area 17 in Visual Imagery: Convergent Evidence from PET and
rTMS.

S. M. Kosslyn, (1,2*) A. Pascual-Leone, (4) O.
Felician, (4) S. Camposano, (4) J. P. Keenan,
(4) W. L. , Thompson, (1) G. Ganis, (1) K. E.
Sukel, (1) N. M. Alpert (3)
 
Visual imagery is used in a wide range of mental activities, ranging from
memory to reasoning, and also plays a role in
perception proper. The contribution of
early visual cortex, specifically Area 17,
to visual mental imagery was examined by the use of two
convergent techniques. In one, subjects closed their eyes
during positron emission tomography (PET)
while they visualized and compared
properties (for example, relative length) of sets of
stripes. The results showed that when
people perform this task, Area 17 is
activated. In the other, repetitive transcranial magnetic
stimulation (rTMS) was applied to medial
occipital cortex before presentation of
the same task. Performance was impaired after rTMS
compared with a sham control condition;
similar results were obtained when the
subjects performed the task by actually looking at the
stimuli. In sum, the PET results showed
that when patterns of stripes are
visualized, Area 17 is activated, and the rTMS results
showed that such activation underlies
information processing.
 
1 Department of Psychology, Harvard University, Cambridge,
MA 02138, USA. 
2 Department of Neurology, 
3 Department of Radiology, Massachusetts
General Hospital, Boston, MA 02114, USA. 
4 Laboratory for Magnetic Brain
Stimulation, Behavioral Neurology Unit, Beth Israel Deaconess Medical
Center, Harvard Medical School, Boston, MA 02215, USA. 
* To whom correspondence should be
addressed. E-mail:
smk@xxxxxxxxxxxxxxx 

Present address: Service de Neurologie et de Neuropsychologie, C.H.U.
Hôpital de la Timone, Marseille, France.


 From the same issue, here's a commentary from page 22:

NEUROBIOLOGY:
Shedding Light on Visual Imagination
Marcia Barinaga
 
Neurobiologists have long puzzled over the question of whether the visual
imagery that occurs when the brain imagines an image works the same way
as when the brain processes a real image from the retina. Results
described on page 167 now suggest that it does. Using transcranial
magnetic stimulation (TMS), which temporarily disrupts the functions of
specific brain areas, a team of neuroscientists found evidence that the
primary visual cortex, the first part of the cerebral cortex to receive
retinal information, is necessary for at least some visual imagery as
well. If TMS works as it seems to, it could provide neuroscientists with
the ability to safely manipulate cognitive processing in humans to help
pin down the functions of the various brain areas. 


Nick

Nicholas V. Cozzi, Ph.D.

Department of Pharmacology

East Carolina University School of Medicine

Greenville, NC  27858