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Selective attention modulates somatosensory cortex organization
NeuroImage
13, Number
6, 2001, Part 2 of 2 Parts 1 b E al@
SENSORIMOTOR
Selective Attention Modulates Somatosensory Cortex Organization Christoph Braun*, Monika Haug*, Katja Wiech*, Niels Birbaumer*t *Institute of Medical Psychology and Behavioral Neurobiology, University of Tuebingen, Germany fGenera1 Psychology, University of Padua, Italy Introduction: Changes in somatosensory afferent input alter the organization of primary somatosensory cortex. Reduced sensory input as after limb amputation results in diminished cortical representational zones (Merzenich et al., 1984), whereas, intensive tactile perceptiontraining causes enlarged representations (Elbert et al. 1995). Not much is known about additional variables affecting the organization of somatosensory cortex. In the present experiment we investigated the effects of selective attention on the functional organization of somatosensory cortex. Methods: Thirteen healthy subjects participated in the study. During the experiment they were stimulated tactilely at the index, middle, ring and little finger of the left hand using four pins, one for each finger. The pins were moved across individual finger tips either from left to right or from right to left. Direction of stimulus motion at a single finger was chosen randomly. Consecutive stimuli were applied to adjacent fingers inducing the sensation of apparent motion across the hand. During condition “Hand” subjects had to attend the direction of apparent motion. In contrast, during condition “Finger” they had to focus their attention to the direction of the stimulus at the index finger. Under both conditions, subjects indicated the direction of the stimulus movement by pressing a button with the right hand. Stimuli during “Finger” and “Hand” conditions were physically identical. Each subject received both conditions in different blocks. Somatosensory evoked magnetic fields were recorded using a whole-head 15 1 channel magnetoencephalograph (CTF Inc). The functional organization of the somatosensory cortex was assessed by neuromagnetic source modeling based on somatosensory evoked magnetic fields. Results: Attending the apparent motion across the hand resulted in a smaller distance between the cortical finger as compared to attending the stimulus direction at a single finger. Results were confirmed after one week.
representation in a repetition
of index and little of the experiment
Conclusion: It is concluded that the functional organization of somatosensory cortex is not exclusively determined by the statistics of afferent input, but also by the direction of attention. As changes in hand representation occur instantaneously it is assumed that the functional organization of somatosensory cortex adapts dynamically to tasks and stimulus context in order to achieve optimal stimulus processing. References: Merzenich MM, Nelson RJ, Stryker MP, Cynader MS, Schoppmann A, Zook JM. Somatosensory cortical map changes following digit amputation in adult monkeys. J Comp Neurol. 1984; 224: 591-605. Elb& T, Pantev C, Wienbmch C, Rockstroh B, Taub E. Increased cortical representation of the fingers of the left hand in string players. Science 1995; 270: 305-307.
s1134
13, Number
6, 2001, Part 2 of 2 Parts 1 b E al@
SENSORIMOTOR
Selective Attention Modulates Somatosensory Cortex Organization Christoph Braun*, Monika Haug*, Katja Wiech*, Niels Birbaumer*t *Institute of Medical Psychology and Behavioral Neurobiology, University of Tuebingen, Germany fGenera1 Psychology, University of Padua, Italy Introduction: Changes in somatosensory afferent input alter the organization of primary somatosensory cortex. Reduced sensory input as after limb amputation results in diminished cortical representational zones (Merzenich et al., 1984), whereas, intensive tactile perceptiontraining causes enlarged representations (Elbert et al. 1995). Not much is known about additional variables affecting the organization of somatosensory cortex. In the present experiment we investigated the effects of selective attention on the functional organization of somatosensory cortex. Methods: Thirteen healthy subjects participated in the study. During the experiment they were stimulated tactilely at the index, middle, ring and little finger of the left hand using four pins, one for each finger. The pins were moved across individual finger tips either from left to right or from right to left. Direction of stimulus motion at a single finger was chosen randomly. Consecutive stimuli were applied to adjacent fingers inducing the sensation of apparent motion across the hand. During condition “Hand” subjects had to attend the direction of apparent motion. In contrast, during condition “Finger” they had to focus their attention to the direction of the stimulus at the index finger. Under both conditions, subjects indicated the direction of the stimulus movement by pressing a button with the right hand. Stimuli during “Finger” and “Hand” conditions were physically identical. Each subject received both conditions in different blocks. Somatosensory evoked magnetic fields were recorded using a whole-head 15 1 channel magnetoencephalograph (CTF Inc). The functional organization of the somatosensory cortex was assessed by neuromagnetic source modeling based on somatosensory evoked magnetic fields. Results: Attending the apparent motion across the hand resulted in a smaller distance between the cortical finger as compared to attending the stimulus direction at a single finger. Results were confirmed after one week.
representation in a repetition
of index and little of the experiment
Conclusion: It is concluded that the functional organization of somatosensory cortex is not exclusively determined by the statistics of afferent input, but also by the direction of attention. As changes in hand representation occur instantaneously it is assumed that the functional organization of somatosensory cortex adapts dynamically to tasks and stimulus context in order to achieve optimal stimulus processing. References: Merzenich MM, Nelson RJ, Stryker MP, Cynader MS, Schoppmann A, Zook JM. Somatosensory cortical map changes following digit amputation in adult monkeys. J Comp Neurol. 1984; 224: 591-605. Elb& T, Pantev C, Wienbmch C, Rockstroh B, Taub E. Increased cortical representation of the fingers of the left hand in string players. Science 1995; 270: 305-307.
s1134