Subdivisions of the working memory system: a high resolution fMRI study

The working memory (WM) system is a system that is able to maintain and
integrate sensory information, long term memory and internal motivational
states in order to flexibly select the appropriate response for a given task or
situation. Many studies have tried to model the way this system works in terms
of regional brain activity, but literature disagrees. In general the discussion
boils down to a domain-specific hypothesis in which the working memory is
organised in domains like verbal, spatial, auditory and object information, and
a function-specific hypothesis, which argues for a subdivision in functions
like maintenance of information, encoding, planning and response selection.
Imaging studies have implicated the prefrontal cortex and some parietal regions
in these working memory processes, and mainly the dorsolateral prefrontal
cortex is active in all working memory tasks. Until recently the imaging
techniques were unable to provide insight in the more detailed workings of this
system though, but with time MRI scanners have improved in spatial and temporal
resolution. Better insights in the origin of the BOLD response in combination
with improved experimental design make it possible to map processes within the
range of milliseconds. For this research we will use high resolution fMRI
technology on a 7T scanner

The main objective of this study is to determine whether the working memory
system works according to a domain specific subdivision and/or a function
specific subdivision, and which brain areas play an important role in these
subdivisions.

This is a case-study assessing working memory using high resolution functional
MRI. Subjects perform a computerized task while functional MRI images are
aquired.

There are no known risks associated with fMRI acquisition. The technique does
not require administration of any contrast agent or ionizing radiation. The
fMRI procedure is painless and not uncomfortable, although it does require the
subject to lie still with the head and part of the body confined in a
tunnel-like device. The Utrecht group has ample experience with fMRI scanning
(400 sessions per year, including children and adolescents). If the subject is
uncomfortable with any aspect of the procedure the study will be terminated. If
the study is terminated, every effort will be taken to ensure that the
experience for the subject is still a positive one.

Subjects will visit once and will participate for about three hours. The time
in the scanner wil be a maximum of one hour. The subject is provided with
earplugs to protect him from the scanner noise. Also MR proof clothing is
provided for the time in the scanner. An intercom is available in the MR
scanner to remain in contact with the subject during the whole session and an
emergency button is placed with the subject with which he can indicate to stop
the procedure immediately. The MR scanner is handled by trained personnel and
subjects are screened for metal before entering the scanner.

This study will provide insight in the way the working memory system works in
human subjects. Finding out the way this WM system works will improve our
understanding of conscious control and can provide insight in diseases in which
WM is impaired like Parkinson*s disease, Alzheimer, schizophrenia and ADHD.