Showing papers by "Gereon R. Fink published in 1997"

Neural activation during selective attention to subjective emotional responses

Abstract: We examined neural activity associated with selectively attending to subjective emotional responses in a study where subjects viewed emotional picture sets. During picture viewing when subjects attended to their subjective emotional responses, highly significant increased neural activity was elicited in rostral anterior cingulate (BA 32) (Z = 6.87, p < 0.001, corrected). By contrast, under the same stimulus conditions when subjects attended to spatial aspects of identical picture sets activation was observed in the parieto-occipital cortex bilaterally (Z = 5.71, p < 0.001, corrected). The findings indicated a specific role for the anterior cingulate cortex in representing subjective emotional responses and are consistent with a suggested role for associated medial prefrontal structures in representing states of mind.

Multiple nonprimary motor areas in the human cortex

Abstract: Fink, Gereon R., Richard S. J. Frackowiak, Uwe Pietrzyk, and Richard E. Passingham. Multiple nonprimary motor areas in the human cortex. J. Neurophysiol. 77: 2164–2174, 1997. We measured the distri...

How the brain learns to see objects and faces in an impoverished context

Abstract: A degraded image of an object or face, which appears meaningless when seen for the first time, is easily recognizable after viewing an undegraded version of the same image The neural mechanisms by which this form of rapid perceptual learning facilitates perception are not well understood Psychological theory suggests the involvement of systems for processing stimulus attributes, spatial attention and feature binding, as well as those involved in visual imagery Here we investigate where and how this rapid perceptual learning is expressed in the human brain by using functional neuroimaging to measure brain activity during exposure to degraded images before and after exposure to the corresponding undegraded versions Perceptual learning of faces or objects enhanced the activity of inferior temporal regions known to be involved in face and object recognition respectively In addition, both face and object learning led to increased activity in medial and lateral parietal regions that have been implicated in attention and visual imagery We observed a strong coupling between the temporal face area and the medial parietal cortex when, and only when, faces were perceived This suggests that perceptual learning involves direct interactions between areas involved in face recognition and those involved in spatial attention, feature binding and memory recall

Neural mechanisms involved in the processing of global and local aspects of hierarchically organized visual stimuli.

Abstract: We investigated the functional anatomy involved in sustaining or switching visual attention between different perceptual levels, using functional imaging measures of neural activity. Two experiments were carried out using hierarchically organized letters (i.e. large letters made out of small letters). In a divided-attention task, subjects were required to switch attention between local and global levels. The number of successive stimuli for which subjects had to sustain attention to either the global or local level co-varied significantly with temporal-parietal activations bilaterally. Other activations were also observed in the right orbitofrontal cortex, the right dorsolateral prefrontal cortex, and the right middle temporal gyrus. The number of switches between levels co-varied significantly with activations in the left supplementary motor area and the left medial parietal cortex. In the directed-attention task, subjects were required to attend to either the global or local level of the stimuli throughout all trials; attention to the global aspect resulted in significant activation of the right lingual gyrus while attention to the local aspect significantly activated the left inferior occipital cortex. We suggest that left hemisphere activations with increasing numbers of switches between perceptual levels reflect increased demands on an executive attentional system, while sustained attention to either level activates a predominantly right hemispheric network involving temporal-parietal and dorsolateral prefrontal regions. Overall, the results provide evidence for relative hemispheric specialization for global and local processing in accordance with previous neuropsychological studies. In addition, the findings demonstrate that early visual processing mechanisms in the prestriate cortex are influenced by an attentional system in temporal-parietal areas.

Space-based and object-based visual attention: shared and specific neural domains.

Abstract: Visual attention can be primarily allocated to either where an object is in space (with little emphasis on the structure of the object itself) or to the structure of the object (with little emphasis on where in space the object is located). Using PET measures of regional cerebral blood flow (rCBF) to index neural activity, we investigated the shared and specific functional anatomy underlying both of these types of visual attention in a controlled non-cueing non-blocked paradigm that involved identical stimuli across the conditions of interest. The interaction of eye movements with these attentional systems was studied by introducing fixation or free vision as an additional factor. Relative to the control condition, object-based and space-based attention showed significant activations of the left and right medial superior parietal cortex and the left lateral inferior parietal cortex, the left prefrontal cortex and the cerebellar vermis. Significant differential activations were observed during object-based attention in the left striate and prestriate cortex. Space-based attention activated the right prefrontal cortex and the right inferior temporal-occipital cortex. Differential neural activity due to free vision or fixation was observed in occipital areas only. Significant interactions of free vision/fixation on activations due to object-based and space-based attention were observed in the right medial superior parietal cortex and left lateral inferior parietal cortex, respectively. The study provides direct evidence for the importance of the parietal cortex in the control of object-based and space-based visual attention. The results show that object-based and space-based attention share common neural mechanisms in the parietal lobes, in addition to task specific mechanisms in early visual processing areas of temporal and occipital cortices.

Hemispheric specialization for global and local processing: the effect of stimulus category

Abstract: Neuropsychological evidence indicates that the global aspect of complex visual scenes is preferentially processed by the right hemisphere, and local aspects are preferentially processed by the left hemisphere. Using letter-based hierarchical stimuli (Navon figures), we recently demonstrated, in a directed-attention task, lateralized neural activity (assessed by positron emission tomography) in the left prestriate cortex during local processing, and in the right prestriate cortex during global processing. Furthermore, temporal-parietal cortex was critically activated bilaterally in a divided-attention task that involved varying the number of target switches between local and global levels of letter-based hierarchical stimuli. Little is known about whether such stimulus categories influence such hemispheric lateralization. We now present data on brain activity, derived from positron emission tomography, in normal subjects scanned during either local or global processing of object-based hierarchical stimuli. We again observe attentional modulation of neural activity in prestriate cortex. There is now greater right-sided activation for local processing and greater left-sided activation for global processing, which is the opposite of that seen with letter-based stimuli. The results suggest that the relative differential hemispheric activations in the prestriate areas during global and local processing are modified by stimulus category.

Cerebral areas associated with motor control of speech in humans

Abstract: We have defined areas in the brain activated during speaking, utilizing positron emission tomography. Six normal subjects continuously repeated the phrase "Buy Bobby a poppy" (requiring minimal language processing) in four ways: A) spoken aloud, B) mouthed silently, C) without articulation, and D) thought silently. Statistical comparison of images from conditions A with C and B with D highlighted areas associated with articulation alone, because control of breathing for speech was controlled for; we found bilateral activations in sensorimotor cortex and cerebellum with right-sided activation in the thalamus/caudate nucleus. Contrasting images from conditions A with B and C with D highlighted areas associated with the control of breathing for speech, vocalization, and hearing, because articulation was controlled for; we found bilateral activations in sensorimotor and motor cortex, close to but distinct from the activations in the preceding contrast, together with activations in thalamus, cerebellum, and supplementary motor area. In neither subtraction was there activation in Broca's area. These results emphasize the bilaterality of the cerebral control of "speaking" without language processing.

A PET Study of Persistent Psychogenic Amnesia Covering the Whole Life Span.

Abstract: A patient with ongoing psychogenic amnesia is described. NN lost his personal identity eight months prior to the reported investigation. All physical and neurological examinations, including magnetic resonance imaging, were unremarkable. Neuropsychological testing revealed above-average intelligence and anterograde memory abilities. No retrograde amnesia for factual knowledge was detected. However, severe persistent amnesia was found for personal events prior to the psychogenic fugue (retrograde episodic amnesia). In contrast, personal episodes subsequent to the fugue were well preserved. For NN, a PET activation study was performed during the following phases: Baseline, a rest or control state; Prefugue, during which sentences containing episodic information of NN's past prior to the fugue were presented; and Postfugue, where episodic information concerned with personal experiences following the fugue was presented. The two activation tasks both led to increases in regional cerebral blood flow in memorya...

Impaired episodic memory retrieval in a case of probable psychogenic amnesia

Abstract: A patient with severe, selective retrograde amnesia for personal material, diagnosed as probable psychogenic amnesia, was investigated intensively neuropsychologically with cranial computed tomography (CCT), magnetic resonance imaging (MRI), and single photon emission tomography (SPECT). The patient was of average intelligence and memory with no anterograde amnesia. No evidence for structural brain damage was detected in CCT and MRI. SPECT, performed about 3 weeks after the onset of symptoms, demonstrated reduced perfusion in right temporal and frontal areas, that is, in areas which have been suggested as critical for episodic memory retrieval. To study episodic memory retrieval, positron-emission-tomography (PET) bloodflow (rCBF) measurements were performed 6 months after the onset of symptoms. During episodic memory retrieval bilateral neuronal activations were observed in the precuneus, the lateral parietal and the right dorsolateral and polar prefrontal cortex. Compared to the results of previous functional imaging studies on episodic memory retrieval, our findings suggest an underlying functional disturbance of brain areas previously demonstrated to be involved in episodic memory retrieval.