Organization of the visual and auditory systems in hemispherectomized patients

There remain important limitations to our knowledge of how the human brain
endows us with perception and how this ability develops and changes with age.
In particular, we have a very limited understanding of the role and cause of
anatomical and functional hemispheric asymmetries (i.e. lateralization) in the
visual and auditory systems. Therefore, we aim to study a unique group of
patients in which one hemisphere is removed or disconnected (hemispherectomized
patients) to gain more insight into the lateralization of the visual and
auditory systems, and the adaptations of these systems after brain damage and
brain surgery. We hypothesize that a) depending on the age of brain damage
onset and on which hemisphere is removed, functions are found in the remaining
hemisphere that are normally expected to be located in the removed hemisphere,
b), the remaining hemisphere has abnormal retinotopic maps and c) functions
that normally require two hemispheres can - to a certain extent - still be
performed following a hemispherectomy.

Our objective is to obtain insight into whether and how the visual and auditory
systems of hemispherectomized patients have adapted after brain damage and
brain surgery in early life. For this purpose we will perform psychophysical
tests and (functional) Magnetic Resonance Imaging ((f)MRI) directed at visual
and auditory functioning. We will relate our findings to the etiology, to the
age at which the brain damage occurred, to the age at which the hemispherectomy
was performed, to the epilepsy duration, and to which hemisphere is removed or
disconnected.

The study will be an observational study; a cross-sectional case-control design
with cases and controls matched for age and gender. The study will contain four
parts: 1) a functional questionnaire, 2) psychophysical measurements, 3) an
(f)MRI experiment, including Diffusion Tensor Imaging, and 4) additional
tests.

There are no risks associated with this study. Participants will be exposed to
standard clinical test and an (f)MRI experiment with a magnetic field of 3
Tesla and fast fluctuating magnetic gradients and radiofrequency fields. These
field strengths are common in fMRI and MRI research. Up till now no side
effects have been reported and hemispherectomy patients have been studied with
fMRI before, also without side effects. In rare cases an abdominal peripheral
nerve will be stimulated because of the fluctuating magnetic fields. This
results in a tickling, but harmless, feeling.