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Felix Blankenburg

Publications and source records attributed to Felix Blankenburg.

12 recordsLinked to original sources
PubMed2006

Neural coding of tactile decisions in the human prefrontal cortex.

The neural processes underlying tactile decisions in the human brain remain elusive. We addressed this question in a functional magnetic resonance imaging study using a somatosensory discrimination task, requiring participants to compare the frequency of two successive tactile stimuli. Tactile stimuli per se engaged somatosensory, parietal, and frontal cortical regions. Using a statistical model that accounted for the relative difference in frequencies (i.e., Weber fraction) and discrimination accuracy (i.e., correct or incorrect), we show that trial-by-trial relative frequency difference is represented linearly by activity changes in the left dorsolateral prefrontal cortex (DLPFC), the dorsal anterior cingulate cortex, and bilateral anterior insular cortices. However, a circumscribed region within the left DLPFC showed a different response pattern expressed as activity changes that were monotonically related to relative stimulation difference only for correct but not for incorrect trials. Our findings suggest that activity in the left DLPFC encodes stimulus representations that underlie veridical tactile decisions in humans.

Adult↗
PubMed2006

Concurrent TMS-fMRI and psychophysics reveal frontal influences on human retinotopic visual cortex.

BACKGROUND: Regions in human frontal cortex may have modulatory top-down influences on retinotopic visual cortex, but to date neuroimaging methods have only been able to provide indirect evidence for such functional interactions between remote but interconnected brain regions. Here we combined transcranial magnetic stimulation (TMS) with concurrent functional magnetic resonance imaging (fMRI), plus psychophysics, to show that stimulation of the right human frontal eye-field (FEF) produced a characteristic topographic pattern of activity changes in retinotopic visual areas V1-V4, with functional consequences for visual perception. RESULTS: FEF TMS led to activity increases for retinotopic representations of the peripheral visual field, but to activity decreases for the central field, in areas V1-V4. These frontal influences on visual cortex occurred in a top-down manner, independently of visual input. TMS of a control site (vertex) did not elicit such visual modulations, and saccades, blinks, or pupil dilation could not account for our results. Finally, the effects of FEF TMS on activity in retinotopic visual cortex led to a behavioral prediction that we confirmed psychophysically by showing that TMS of the frontal site (again compared with vertex) enhanced perceived contrast for peripheral relative to central visual stimuli. CONCLUSIONS: Our results provide causal evidence that circuits originating in the human FEF can modulate activity in retinotopic visual cortex, in a manner that differentiates the central and peripheral visual field, with functional consequences for perception. More generally, our study illustrates how the new approach of concurrent TMS-fMRI can now reveal causal interactions between remote but interconnected areas of the human brain.

Adult↗
PubMed2006

The cutaneous rabbit illusion affects human primary sensory cortex somatotopically.

We used functional magnetic resonance imaging (fMRI) to study neural correlates of a robust somatosensory illusion that can dissociate tactile perception from physical stimulation. Repeated rapid stimulation at the wrist, then near the elbow, can create the illusion of touches at intervening locations along the arm, as if a rabbit hopped along it. We examined brain activity in humans using fMRI, with improved spatial resolution, during this version of the classic cutaneous rabbit illusion. As compared with control stimulation at the same skin sites (but in a different order that did not induce the illusion), illusory sequences activated contralateral primary somatosensory cortex, at a somatotopic location corresponding to the filled-in illusory perception on the forearm. Moreover, the amplitude of this somatosensory activation was comparable to that for veridical stimulation including the intervening position on the arm. The illusion additionally activated areas of premotor and prefrontal cortex. These results provide direct evidence that illusory somatosensory percepts can affect primary somatosensory cortex in a manner that corresponds somatotopically to the illusory percept.

Adult↗
PubMed2006

Repetitive transcranial magnetic stimulation-induced changes in sensorimotor coupling parallel improvements of somatosensation in humans.

Repetitive transcranial magnetic stimulation (rTMS) is an established technique for non-invasive stimulation of human cortex. Although studies have shown an influence of rTMS on single cortical regions and on simple behavioral response patterns, its influences on the dynamics of task-related activity in cortical networks have not been characterized. We provide such a characterization by showing that 5 Hz rTMS over primary somatosensory cortex (SI) induces a reconfiguration of activity patterns in a sensorimotor network, comprising the stimulated region and ipsilateral primary motor cortex (MI). These plastic changes endure for up to 120 min and are correlated with behavioral improvement in discrimination. Dynamic causal modeling showed that this reconfiguration could be explained by an rTMS-induced increase in SI excitability (self-connection) and an increase in the effective connectivity from SI to MI. Thus, our data demonstrate that rTMS can temporarily induce behaviorally relevant reorganization within a complex cortical network underlying human somatosensory experience.

Adult↗
PubMed2006

Neural correlates of crossmodal visual-tactile extinction and of tactile awareness revealed by fMRI in a right-hemisphere stroke patient.

We used fMRI to study the neural correlates of crossmodal, visual-tactile extinction in a single case (patient GK). GK has chronic extinction after a lesion centred on right inferior parietal cortex, and has previously been investigated extensively in purely visual fMRI studies [e.g. Rees, G., Wojciulik, E., Clarke, K., Husain, M., Frith, C., & Driver, J. (2000). Unconscious activation of visual cortex in the damaged right hemisphere of a parietal patient with extinction. Brain, 123(Pt 8), 1624-1633; Rees, G., Kreiman, G., & Koch, C. (2002). Neural correlates of consciousness in humans. Nature Reviews Neuroscience, 3(4), 261-270]. With concurrent stimulation of the right visual field plus left index finger, GK showed crossmodal extinction of left touch on approximately half of such trials here (reflecting impaired sensitivity, i.e. lowered d-prime), albeit becoming aware of left touch on the other half. fMRI revealed activation of contralateral primary somatosensory cortex on crossmodal trials when touch was extinguished from awareness, suggesting unconscious residual processing there. When GK became aware of the left touch, additional activation was found in surviving right parietal cortex, and in frontal regions; moreover, functional coupling was enhanced with a region of frontal cortex implicated in awareness by previous work. Finally, on trials where crossmodal extinction arose, surviving right parietal cortex showed stronger functional coupling with the left visual and right somatosensory regions driven by the competing stimuli, indicating that crossmodal extinction arises when inputs to separate modalities interact competitively via multimodal cortex.

Aged↗
PubMed2006

Now you feel it--now you don't: ERP correlates of somatosensory awareness.

We investigated correlates of somatosensory awareness for supra theshold stimuli using event-related potentials in a masking paradigm: Conscious perception of a weak, but suprathreshold "target" stimulus was suppressed in a significant number of trials when followed by a higher-intensity "mask" stimulus. ERPs were compared for trials with perceived versus unperceived target stimuli. Early ERPs (P60, N80), generated in the contralateral S1, were found independent of stimulus perception. In contrast, for consciously perceived target stimuli, amplitude enhancements were observed for the P100 and N140. Thus, early activation of S1 is not sufficient to warrant conscious stimulus perception. Conscious stimulus processing differs significantly from unconscious processing starting around 100 ms after stimulus presentation when the signal is processed in parietal and frontal cortices, brain regions crucial for stimulus access into conscious perception.

Adult↗
PubMed2005

Preserved responsiveness of secondary somatosensory cortex in patients with thalamic stroke.

Cortical representations may change when somatosensory input is altered. Here, we investigated the functional consequences of partial "central" deafferentation of the somatosensory cortex due to a lesion of the ventroposterior lateral nucleus (VPL) in patients at a chronic stage after solitary infarction of the thalamus. Event-related functional magnetic resonance imaging during electrical index finger stimulation of the affected and nonaffected side was performed in 6 patients exhibiting contralesional sensory deficits (mainly hypesthesia). Involvement of the VPL and additional nuclei was determined by high-resolution magnetic resonance imaging (MRI) and subsequent MRI-to-atlas coregistration. For the group, statistical parametric maps showed a reduced activation of contralateral primary somatosensory cortex (SI) in response to stimulation of the affected side. However, no significant difference in the activation of contralateral secondary somatosensory cortex (SII) compared with stimulation of the nonaffected side was detected. Correspondingly, the ratio of SII-to-SI activation for the ipsilesional hemisphere was markedly elevated as compared with the contralesional hemisphere. For preserved responsiveness of SII in thalamic stroke comparable with that of the contralesional hemisphere, possible explanations are a direct thalamocortical input to SII mediating parallel information processing, nonlinear response behavior of SII in serial processing, or reorganizational processes that evolved over time.

Aged↗
PubMed2005

Sub-area-specific Suppressive Interaction in the BOLD responses to simultaneous finger stimulation in human primary somatosensory cortex: evidence for increasing rostral-to-caudal convergence.

In the primary somatosensory cortex (SI) of non-human primates, receptive field properties have been shown to differ between its sub-areas with increasing convergence in areas 1 and 2 as compared with area 3b. In this study, we searched for a similar functional organization of human SI. We performed fMRI in healthy subjects during separate or simultaneous electrical stimulation of the second and third finger of the right hand. Activation patterns in response to stimulation of single fingers reflected the somatotopical arrangement within the hand area of SI. Somatotopy was more clear-cut in area 3b as compared with areas 1 and 2. The response to simultaneous stimulation was considerably smaller than the summed responses to separate stimulation of each finger alone, pointing to a suppressive interaction effect. A region-of-interest analysis in the representational areas of the second and third finger revealed sub-area-specific differential suppressive interaction with an increase along the rostral-caudal axis (areas 3b, 1 and 2: 26, 32.7 and 42.2%, respectively). These findings on differences in the topographic as well as functional organization between sub-areas of SI support the notion of increasing convergence and integration from area 3b to areas 1 and 2 in human subjects.

Adult↗
PubMed2003

Correlates of alpha rhythm in functional magnetic resonance imaging and near infrared spectroscopy.

We used simultaneous electroencephalogram-functional magnetic resonance imaging (EEG-fMRI) and EEG-near infrared spectroscopy (NIRS) to investigate whether changes of the posterior EEG alpha rhythm are correlated with changes in local cerebral blood oxygenation. Cross-correlation analysis of slowly fluctuating, spontaneous rhythms in the EEG and the fMRI signal revealed an inverse relationship between alpha activity and the fMRI-blood oxygen level dependent signal in the occipital cortex. The NIRS-EEG measurements demonstrated a positive cross-correlation in occipital cortex between alpha activity and concentration changes of deoxygenated hemoglobin, which peaked at a relative shift of about 8 s. Our data suggest that alpha activity in the occipital cortex is associated with metabolic deactivation. Mapping of spontaneously synchronizing distributed neuronal networks is thus shown to be feasible.

Adult↗
PubMed2003

Evidence for a rostral-to-caudal somatotopic organization in human primary somatosensory cortex with mirror-reversal in areas 3b and 1.

Medial-to-lateral somatotopy is a well-established feature of the human primary somatosensory cortex (SI); however, it is unknown whether, similarly to non-human primates, a rostral-to-caudal somatotopic arrangement exists as well. Therefore, in this functional magnetic resonance imaging (fMRI) study on eight healthy human subjects, five circumscribed skin areas sequentially located on the third finger and the palm of the hand were stimulated with innocuous electrical pulses. Within area 3b of contralateral SI, successive cortical representation sites ordered in a rostral-to-caudal fashion were seen in the group analysis and in six individual subjects. The fingertip was located most rostrally, whereas the proximal parts of the finger as well as the distal palm were represented at more caudal locations. Within area 1, the group analysis revealed a similar pattern of discrete representations. However, in contrast to area 3b, the fingertip was located most caudally, whereas the more proximal parts of the finger were found to be represented rostrally within area 1. Thus, the representation pattern of area 1 appeared as a 'mirror image' of that of area 3b. In comparison to the representations of the finger and the distal palm, the proximal palm was found to be represented at a more medial position of the postcentral gyrus.

Adult↗
PubMed2002

Event-related fMRI of the somatosensory system using electrical finger stimulation.

Cortical signal intensity changes due to brief (1 s) innocuous electrical stimuli applied to the second and fifth finger of the right hand were measured by means of fMRI at 1.5 T. The activation pattern in this event-related fMRI approach closely resembled that obtained in recent block-design studies. Activations were found in contralateral primary (SI) and bilaterally in secondary (SII) somato-sensory cortex as well as in posterior parietal cortex, insula, and supplementary motor area (SMA). In SI, the somatotopic organization of the hand area is demonstrated, more clearly to be seen in area 3b than in area 1 and 2. In conclusion, the feasibility to employ event-related somatosensory stimulation paradigms in fMRI studies is demonstrated.

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