APRIXIA : IMPAIRED BRAIN NETWORK FOR USING TOOLS
Researchers from Technische Universität München
(TUM) and the Klinikum rechts der Isar hospital have analyzed the brain
networks that control the use of tools or other utensils. Their chosen method
of functional magnetic resonance imaging (fMRI) shows the areas of the brain
that are activated when a person thinks, moves and performs actions.
The use of tools is an
essential human skill. "Numerous studies are investigating the neural
processes at play when we pick up a tool," says Prof. Joachim Hermsdörfer
from TUM's Chair of Human Movement Science. "But many of these studies are
restricted to test subjects observing an action, miming it, or simply
visualizing it." The aim of this latest study was to analyze the basic
neural principles of tool use under the most realistic conditions possible.
In the MRI study, the
subjects received ten everyday objects, including a hammer, a bottle-opener, a
key, a lighter and a scissors as well as some unfamiliar objects. Their task
was to either use the objects or simply lift them up and place them down again,
first with the left and then with the right hand. When they analyzed the data,
the scientists looked at the planning phase and the actual execution phase
separately. In this way, they were able to identify the brain networks that
were activated while the subjects planned and used a tool and those that
controlled execution.
Tool-specific network
in the brain
One important finding
was that the left hemisphere was activated when the subjects planned to use a
tool -- regardless of the hand they held it in. In addition, the researchers
recognized a distributed network responsible for both planning and execution.
When working with unfamiliar objects, these regions of the brain were less
activated.
The "tool
network" consists of brain regions of the parietal and frontal lobes as
well as regions in the posterior temporal lobe and another area in the lateral
occipital lobe. What the researchers found, therefore, was a neural activation
pattern that covered all elements of a complex action. This includes recognizing
the objects as tools, understanding how they are used, and the motor action to
actually use the tool.
"The study also
allowed us to confirm that there are different streams of perception in the
brain for different tasks," explains Hermsdörfer. The dorsal stream of
perception conducts signals to the posterior parietal lobe and is generally
responsible for controlling actions. "It can be divided into two
function-specific processing pathways. The dorso-dorsal stream controls basic
gripping and movement processes, regardless of whether the person is familiar
with the object or not. A second ventro-dorsal stream becomes active when we
use tools that are familiar to us.
Armed with knowledge
about the localization of these "action modules," doctors could in
future provide a more differentiated diagnosis of apraxia and develop improved
therapeutic approaches.
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