Showing papers by "Gereon R. Fink published in 1999"

The neural consequences of conflict between intention and the senses

Abstract: Normal sensorimotor states involve integration of intention, action and sensory feedback. An example is the congruence between motor intention and sensory experience (both proprioceptive and visual) when we move a limb through space. Such goal-directed action necessitates a mechanism that monitors sensorimotor inputs to ensure that motor outputs are congruent with current intentions. Monitoring in this sense is usually implicit and automatic but becomes conscious whenever there is a mismatch between expected and realized sensorimotor states. To investigate how the latter type of monitoring is achieved we conducted three fully factorial functional neuroimaging experiments using PET measures of relative regional cerebral blood flow with healthy volunteers. In the first experiment subjects were asked to perform Luria's bimanual co-ordination task which involves either in-phase (conditions 1 and 3) or out-of-phase (conditions 2 and 4) bimanual movements (factor one), while looking towards their left hand. In half of the conditions (conditions 3 and 4) a mirror was used that altered visual feedback (factor two) by replacing their left hand with the mirror image of their right hand. Hence (in the critical condition 4) subjects saw in-phase movements despite performing out-of-phase movements. This mismatch between intention, proprioception and visual feedback engendered cognitive conflict. The main effect of out-of-phase movements was associated with increased neural activity in posterior parietal cortex (PPC) bilaterally [Brodmann area (BA) 40, extending into BA 7] and dorsolateral prefrontal cortex (DLPFC) bilaterally (BA 9/46). The main effect of the mirror showed increased neural activity in right DLPFC (BA 9/46) and right superior PPC (BA 7) only. Analysis of the critical interaction revealed that the mismatch condition led to a specific activation in the right DLPFC alone (BA 9/46). Study 2, using an identical experimental set-up but manipulating visual feedback from the right hand (instead of the left), subsequently demonstrated that this right DLPFC activation was independent of the hand attended. Finally, study 3 removed the motor intentional component by moving the subjects' hand passively, thus engendering a mismatch between proprioception and vision only. Activation in the right lateral prefrontal cortex was now more ventral than in studies 1 or 2 (BA 44/45). A direct comparison of studies 1 and 3 (which both manipulated visual feedback from the left hand) confirmed that a ventral right lateral prefrontal region is primarily activated by discrepancies between signals from sensory systems, while a more dorsal area in right lateral prefrontal cortex is activated when actions must be maintained in the face of a conflict between intention and sensory outcome.

Contrast polarity and face recognition in the human fusiform gyrus

Abstract: Functional imaging has revealed face-responsive visual areas in the human fusiform gyrus, but their role in recognizing familiar individuals remains controversial. Face recognition is particularly impaired by reversing contrast polarity of the image, even though this preserves all edges and spatial frequencies. Here, combined influences of familiarity and priming on face processing were examined as contrast polarity was manipulated. Our fMRI results show that bilateral posterior areas in fusiform gyrus responded more strongly for faces with positive than with negative contrast polarity. An anterior, right-lateralized fusiform region is activated when a given face stimulus becomes recognizable as a well-known individual.

Cortical and subcortical control of tongue movement in humans: a functional neuroimaging study using fMRI

Abstract: We have used voluntary tongue contraction to test whether we can image activation of the hypoglossal nuclei within the human brain stem by using functional magnetic resonance imaging (fMRI). Functional images of the whole brain were acquired in eight subjects by using T2-weighted echo planar imaging (blood oxygen level development) every 6.2 s. Sequences of images were acquired during 12 periods of 31-s "isometric" rhythmic tongue contraction alternated with 12 periods of 31-s tongue relaxation. Noise arising from cardiac- and respiratory-related movement was removed either by filtration (high pass; cutoff 120 s) or by inclusion in the statistical analysis as confounding effects of no interest. For the group, tongue contraction was associated with significant signal increases (P < 0.05 corrected for multiple comparisons) in the sensorimotor cortex, supplementary motor area, operculum, insula, thalamus, and cerebellum. For the group and for six of eight individuals, significant signal increases were also seen within the medulla (P < 0.001, predefined region of interest with no correction for multiple comparisons); this signal is most likely to reflect neuronal activation associated with the hypoglossal motor nuclei. The data demonstrate that fMRI can be used to detect, simultaneously, the cerebral and brain stem control of tongue movement.