They have been able to demonstrate that inhibitory influences of neighbouring “finger nerve cells” affect the reaction time of a finger. The fingers on the outside – in example the thumb and little finger - therefore react faster than the middle finger, which is exposed to the “cross fire” of two neighbours on each side. Through targeted learning, this speed handicap can be compensated.
The researchers set subjects a simple task to measure the speed of decision: they showed them an image on a monitor that represented all ten fingers. If one of the fingers was marked, the subjects were to press a corresponding key as quickly as possible with that finger. The thumb and little finger were the fastest. The middle finger brought up the rear. “You might think that this has anatomical reasons or depends on the exercise” said Doktor Hubert Dinse, “but we were able to rule that out through further tests. In principle, each finger is able to react equally quickly. Only in the selection task, the middle finger is at a distinct disadvantage.”
To explain their observations, the researchers used computer simulations based on a so-called mean-field model. It is especially suited for modelling large neuronal networks in the brain. For these simulations, each individual finger is represented by a group of nerve cells, which are arranged in the form of a topographic map of the fingers based on the actual conditions in the somatosensory cortex of the brain. “Adjacent fingers are adjacent in the brain too, and thus also in the simulation”, explained Dinse. The communication of the nerve cells amongst themselves is organised so that the nerve cells interact through mutual excitation and inhibition.
The computer simulations showed that the longer reaction time of the middle finger in a multiple choice task is a consequence of the fact that the middle finger is within the inhibition range of the two adjacent fingers. The thumb and little finger on the other hand only receive an inhibitory effect of comparable strength from one adjacent finger each. “In other words, the high level of inhibition received by the nerve cells of the middle fingers mean that it takes longer for the excitement to build up – they therefore react more slowly” said Dinse.
MEDICA.de; Source: Ruhr-Universität Bochum