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R S Frackowiak

Publications and source records attributed to R S Frackowiak.

At least 145 records · Page 8Linked to original sources
PubMed1994

Human cortical areas selectively activated by apparent sound movement.

BACKGROUND: Positron emission tomography (PET) measures cerebral blood flow, an indicator of neural activity. PET has been used successfully to identify visual association areas in the human brain, which are involved in the analysis of different aspects of visual stimuli. However, comparable studies have not yet been carried out for the human auditory system. RESULTS: We have attempted to identify human cortical areas that are selectively activated during sound movement analysis. Using PET, we have identified cortical areas that appeared to be selectively activated while human subjects attended to the position of a moving sound image compared to when they attended to a stationary sound image. The areas are in the right insula, adjacent to the right posterior cingulate, and in the cerebellum. CONCLUSIONS: We suggest that the insula may be acting as an auditory association cortex involved in sound movement analysis, analogous to area V5 in the visual system.

Acoustic Stimulation↗
PubMed1994

The timing of visual evoked potential activity in human area V4.

Studies of human occipital visual cortex have demonstrated functional specializations for colour and for motion, with a pivotal area for colour processing (area V4) being located in the fusiform gyrus. To study the timing of arrival of signals in area V4 we have recorded multi-channel visual evoked potentials (VEPS) to colour and grey 'Mondrian' stimuli, spatio-temporal dipole source analysis being computed on two independent group averages of five and six subjects respectively. Three active brain regions were identified, which we interpret to correspond to areas V1, V2 and V4; they showed sequential but overlapping activity in time with no difference in magnitude between colour and grey stimulated VEPs. Source analysis of the difference potentials, colour minus grey, isolated source activity resulting from colour stimulation and located it in the region of area V4. Activity in area V4 started at 100 ms and peaked at 135 ms after the onset of the visual stimulus.

Adult↗
PubMed1994

Central nervous pathways mediating angina pectoris.

The central nervous pathways of angina pectoris have never been identified in vivo in man. We used positron emission tomography to examine the changes in regional cerebral blood flow associated with angina pectoris. Dynamic positron emission tomography with 15O-labelled water was used in 12 patients with angina and angiographically proven coronary artery disease to measure regional cerebral blood flow changes during angina induced by intravenous dobutamine. All subjects had typical retrosternal chest pain accompanied by ischaemic electrocardiographic changes during dobutamine infusion. Compared to the resting state, angina was associated with increased regional cerebral blood flow in the hypothalamus (percentage change in regional cerebral blood flow +6.5 and Z score 7.2) periaquaductal grey (+2.6 and 4.0), bilaterally in the thalamus (left: +2.7 and 4.3; right +3.7 and 4.7) and lateral prefrontal cortex (left +11.5 and 7.6; right +8.5 and 7.8) and left inferior anterocaudal cingulate cortex (+9.4 and 6.6). In contrast, it was reduced bilaterally in the mid-rostrocaudal cingulate cortex (left -3.7 and 6.3; right -4.7 and 4.6) and fusiform gyrus (left -3.2 and 4.0; right -3.3 and 3.7), right posterior cingulate (-3.9 and 5.8) and left parietal cortices (-4.8 and 6.3). Several minutes after stopping dobutamine infusion, when the patients no longer experienced angina and the electrocardiographic changes had resolved, thalamic, but not cortical activation could be seen. We propose that the central structures activated constitute the pathways for perception of anginal pain and that the thalamus may act as a gate to afferent pain signals, with cortical activation being necessary for the sensation of pain. This method of investigation may form a basis for research into anomalies of visceral pain perception such as silent myocardial ischaemia.

Adult↗
PubMed1994

Brain regions associated with acquisition and retrieval of verbal episodic memory.

It is widely held that conscious recall of past experiences involves a specific system--episodic memory. Patients with amnesia have gross impairments of episodic memory while other kinds of memory remain intact, suggesting that a separable brain system underlies episodic memory. We have used positron emission tomography (PET) to identify components of this system in normal volunteers. A dual-task interference paradigm was used to isolate brain areas associated with acquisition, and a cueing paradigm to isolate the areas concerned with retrieval from verbal episodic memory. Acquisition was associated with activity in the left prefrontal cortex and the retrosplenial area, whereas retrieval was associated with activity in right prefrontal cortex and the precuneus. Our results provide clear evidence that episodic memory involves a network of specific prefrontal and posterior structures which can be fractionated into different component processes.

Brain↗
PubMed1994

Identification of the central vestibular projections in man: a positron emission tomography activation study.

The cerebral representation of space depends on the integration of many different sensory inputs. The vestibular system provides one such input and its dysfunction can cause profound spatial disorientation. Using positron emission tomography (PET), we measured regional cerebral perfusion with various vestibular stimulations to map central vestibular projections and to investigate the cerebral basis of spatial disorientation. We showed that the temporoparietal cortex, the insula, the putamen, and the anterior cingulate cortex are the cerebral projections of the vestibular system in man and that the spatial disorientation caused by unilateral vestibular stimulation is associated with their asymmetric activation.

Adult↗
PubMed1994

Functional mapping of verbal memory and language.

Francis O. Schmitt wrote in his introduction to The Mindful Brain that 'Many theories of higher brain function (learning, memory, perception, self-awareness, consciousness) have been proposed; but in general these lack cogency with respect to the established anatomical and physiological facts and are without biophysical and biochemical plausibility'. A central aim of functional mapping studies of the human brain is a physiological and anatomical description of the brain regions that participate in different brain functions. Language and memory have become, with the advent of modern imaging technologies, the subject of a comparatively large number of mapping studies in recent years. The quality of the data and of the experimental design continue to evolve so that sophisticated questions are being addressed, and convergent findings are now being reported. This article will critically review mapping studies of language and memory and assess how they advance our knowledge of the functional organization of these human faculties.

Brain↗
PubMed1994

Neuropsychological dysfunction in depression: the relationship to regional cerebral blood flow.

The relationship between neuropsychological test performance and regional cerebral blood flow (rCBF) was examined in 29 patients meeting Research Diagnostic Criteria (RDC) for major depression. Following a comprehensive neuropsychological assessment two subsets of tests, comprising tests that discriminated between patients and controls or between patients with varying degrees of global cognitive impairment, were selected. These subtests were entered into a principal components analysis (PCA) which generated a two-factor solution, accounting for 50% of the overall variance in test scores. Individual patient loadings on each of these factors were subsequently correlated with regional cerebral blood flow (rCBF), as measured by positron emission tomography (PET). Both factors demonstrated significant correlations with rCBF in the medial prefrontal cortex and frontal polar cortex while for each factor there were also unique patterns of correlations with posterior brain regions. The findings provide additional evidence that neuropsychological deficits in depression are associated with abnormalities in regional brain function and in particular with the function of the medial prefrontal cortex.

Adult↗
PubMed1994

Imaging transient, randomly occurring neuropsychological events in single subjects with positron emission tomography: an event-related count rate correlational analysis.

Many neuropsychiatric symptom states are idiosyncratic, involuntary, randomly occurring, subjective, and transient. The brain states associated with these clinically important mental states cannot be imaged directly with existing positron emission tomography (PET) techniques. A new PET method that brings such mental/brain states under experimental control for analysis in single subjects is described. It utilizes a slow bolus H2 15O three-dimensional (3D) regional CBF imaging technique. The analysis focuses upon natural or experimentally induced variance in the temporal distribution of specific neuropsychological events over the course of a study session. For each scan, the amount of radioactivity entering the brain during these events is calculated to derive a score reflecting the contribution of the events to the image. A statistical analysis is then performed to identify those pixels in which the intensity covaries with the scan scores over the subject's scans. This permits the identification of the brain areas associated with the mental state of interest. The method is validated using an auditory sentence-monitoring task. The detection in single subjects of cerebral activations associated with recurrent events as brief as 2 s in duration is demonstrated. This method may be used as a means of imaging ephemeral neurologic or neuropsychiatric symptom states or as an alternative to a subtraction design for activation studies.

Adult↗
PubMed1994

A PET study of cognitive strategies in normal subjects during language tasks. Influence of phonetic ambiguity and sequence processing on phoneme monitoring.

We previously demonstrated using PET in normal subjects (Démonet et al., Brain 1992; 115: 1753-68) that, by comparison to a reference task of monitoring for pure tones, a phoneme monitoring task involving two factors of complexity (sequence processing and perceptual ambiguity) activated Wernicke's area and Broca's area. In the present experiment, we explored the respective influence of these factors on brain activation. In addition to the reference task, four phoneme monitoring tasks in non-words were used with stimuli presented binaurally. These included an easy, non-sequential, unambiguous task; a perceptually ambiguous, but non-sequential task; a sequential, but perceptually unambiguous task; a sequential and ambiguous task identical to the one we used in our previous study. Changes in regional cerebral blood flow were measured in nine right-handed volunteers using PET and infusion of H2(15)O. The sequential unambiguous task was associated with the same pattern of activation as that observed for the equivalent non-sequential task, i.e. activation of Wernicke's area. The two tasks with perceptual ambiguity gave rise to activations in the left fusiform gyrus and in Broca's area, respectively. Activation of the left fusiform gyrus in the perceptually ambiguous but non-sequential task suggests a prominent role for a strategy involving phoneme-to-grapheme transcoding in subjects, who thereby attempted to visualize non-words that they could not decipher auditorily. Activation of Broca's area in the sequential and ambiguous task reproduces our previous result and suggests that subjects resorted to a predominantly verbal rehearsal strategy when performing this task.

Adult↗
PubMed1994

The brain activity related to residual motion vision in a patient with bilateral lesions of V5.

We have used the technique of PET to chart the cortical areas activated by visual motion in the brain of a patient with a severe impairment in the ability to recognize the motion of objects (akinetopsia), following bilateral lesions which have so far been presumed to include area V5. High resolution MRI of her brain showed that the zone occupied by area V5 had indeed been destroyed bilaterally. Positron emission tomography activation images, co-registered to the MRIs, showed three principal regions of the cortex activated by motion. These were located (i) bilaterally in the precuneus of superior parietal cortex (area 7 of Brodmann); (ii) bilaterally in the cuneus (a region considered to represent upper V3); (iii) in the left lingual and fusiform gyri (possibly lower V3 and adjacent areas). In contrast to normal subjects, there was no significant activation of area V1 or V2. The stimuli used for scanning were chosen by prior testing of the patient's visual capacities. The control stimulus was a static random distribution of light squares on a dark background. In the moving stimulus these squares moved coherently, the direction of motion changing periodically between the cardinal directions (left, right, up and down). It was ascertained that the patient could correctly identify these directions. We also found (i) that her occasional errors were always in the direction opposite to the motion presented, so that her identification of axis of motion (i.e. vertical or horizontal) was 100% correct; (ii) that when a few static squares were added to the moving the display her identification of direction fell to chance but her identification of the axis of motion remained 100%; (iii) that when a few squares moving opposite and orthogonal to the predominant direction of motion were incorporated, her performance on both direction and axis fell to chance; (iv) that she was unable to identify motion in oblique directions between the horizontal or vertical axes, always guessing one of the cardinal directions. In accounting for her residual vision in terms of cortex, which remains active, we hypothesize; (i) that the bilateral loss of V5 has affected direction sensitive mechanisms at other sites in the cortex which are interconnected with V5 and (ii) that in consequence her performance on our tests reflects the properties of dynamic orientation selective mechanisms that were also differentially activated by the stimuli used during scanning.

Adult↗
PubMed1994

The cerebral activity related to the visual perception of forward motion in depth.

We have used the technique of PET to chart the areas of human cerebral cortex specifically responsive to an optical flow stimulus simulating forward motion in depth over a flat horizontal surface. The optical flow display contained about 2000 dots accelerating in radial directions away from the focus of expansion, which subjects fixated at the centre of the display monitor. Dots remained of constant size, but their density decreased from the horizon, lying across the middle of the screen, to the foreground at the lower screen margin; the top half of the display was void. For the control stimulus the dot motions were randomized, removing any sensation of motion in depth and diminishing the impression of a flat terrain. Comparison of the regional cerebral blood flow (rCBF) elicited by the optical flow and control stimuli was thus intended to reveal any area selectively responsive to the radial velocity field that is characteristic of optical flow in its simplest natural form. Six subjects were scanned, and analysed as a group. Four subjects were analysed as individuals, their PET data being co-registered with MRIs of the cerebrum to localize rCBF changes to individual gyri and sulci. There were three main areas of activation associated with optical flow: the dorsal cuneus (area V3) and the latero-posterior precuneus (or superior parietal lobe) in the right hemisphere, and the occipito-temporal ventral surface, in the region of the fusiform gyrus, in both hemispheres. There was no significant activation of V1/V2, nor of V5. These results show that higher stages of motion take place in both the 'dorsal' and 'ventral' visual pathways, as these are commonly conceived, and that both may be fed by area V3. The information potentially derivable from optical flow concerns the direction of heading, and the layout of the visual environment, a form of three-dimensional structure-from-motion. The perceptual division of labour between the various activated areas cannot be directly inferred, though it is a reasonable supposition that the parietal activation reflects the utility of optic flow for guiding self-motion.

Adult↗
PubMed1994

Cortical control of saccades and fixation in man. A PET study.

To identify cortical regions activated during saccades and visual fixation, regional cerebral blood flow (rCBF) was measured in eight healthy subjects using C15O2 PET during the performance of three tasks: (i) central fixation; (ii) reflexive saccades to random targets; (iii) remembered saccades to locations of recent target appearance. Significant rCBF increases were identified using analysis of covariance and the t statistic (P < 0.001). Compared with central fixation there was activation of striate and extra-striate cortex, posterior parietal cortex (PPC) and frontal eye fields (FEF) during both reflexive and remembered saccades. During remembered saccades there was additional activation of supplementary motor area (SMA), insula, cingulate, thalamus, midbrain, cerebellum and right superior temporal gyrus (Brodmann's area 22). Compared with the individual saccadic tasks, central fixation activated extensive regions of ventromedial (areas 10, 11 and 32) and anterolateral (areas 8, 9, 10, 45 and 46) prefrontal cortex, and foveal visual cortex. We conclude that FEF and PPC are associated with the generation of both reflexive and remembered saccades, with SMA additionally involved during remembered saccades. Sustained voluntary fixation is mediated by prefrontal cortex.

Adult↗
PubMed1994

The role of the right hemisphere in the interpretation of figurative aspects of language. A positron emission tomography activation study.

We investigated cerebral activity in six normal volunteers using PET to explore the hypothesis that the right hemisphere has a specific role in the interpretation of figurative aspects of language such as metaphors. We also mapped the anatomical structures involved in sentence comprehension. During regional cerebral blood flow measurement subjects were asked to perform three different linguistic tasks: (i) metaphorical comprehension; (ii) literal comprehension of sentences; and (iii) a lexical-decision task. We found that comprehension of sentences compared with the lexical-decision task, induced extensive activation in several regions of the left hemisphere, including the prefrontal and basal frontal cortex, the middle and inferior temporal gyri and temporal pole, the parietal cortex and the precuneus. Comprehension of metaphors was associated with similar activations in the left hemisphere, but in addition, a number of sites were activated in the right hemisphere: the prefrontal cortex, the middle temporal gyrus, the precuneus and the posterior cingulate. We conclude that the interpretation of language involves widespread distributed systems bilaterally with the right hemisphere having a special role in the appreciation of metaphors.

Adult↗
PubMed1994

Brain activity during reading. The effects of exposure duration and task.

Brain activity during reading tasks was investigated using PET. The aim was to account for differences in the results of two previous studies [those of Petersen et al. (Science 1990; 249: 1041-4) and Howard et al. (Brain 1992; 115: 1769-82)] by systematically varying the type of reading task and the exposure duration of the word stimuli. Both variables strongly influenced patterns of brain activity. There were three types of task: (i) reading aloud; (ii) reading silently; and (iii) lexical decision on visually presented words and pseudowords. Reading aloud and reading silently engaged the left middle and superior temporal regions, confirming the important role of these areas in visual word processing. The areas principally engaged during lexical decision were the left inferior and middle frontal cortices and the supplementary motor area; activity in these areas suggests that the subjects were using a phonological strategy to perform the task. There was also a significant effect of exposure duration, with activity being greater for short (150 ms) exposure durations than for long (1000 ms or 981 ms) exposure durations. We conclude that until we understand how subtle variations in experimental design influence brain activity during reading tasks, the association of specific processing functions with individual anatomical areas activated during reading is premature.

Adult↗
PubMed1994

A graded task approach to the functional mapping of brain areas implicated in auditory-verbal memory.

Positron emission tomography measurements of regional cerebral blood flow (rCBF) were performed in normal volunteers during a graded auditory-verbal memory task. Subjects were required to remember and then immediately, and freely, recall a series of auditorily presented word lists varying from two to 13 words in length. Significant regional correlations between rCBF and memory load (word list length) were identified using statistical parametric mapping. Increasing memory load correlated with increasing rCBF in the cerebellar vermis and hemispheres, thalamus bilaterally, the superior and middle frontal gyri bilaterally, anterior insular regions bilaterally, anterior cingulate, precuneus and left and right lateral premotor areas. Increasing memory load also correlated with decreasing rCBF in the left and right superior temporal/insular regions, medial frontal gyrus, Brodmann's area 37 bilaterally, cuneus, inferior parietal lobule bilaterally and the mid-portion of the cingulate cortex. The pattern of rCBF change closely resembled that identified in a previously reported study using a cognitive subtraction paradigm and provides further evidence for a widespread neural system subserving auditory-verbal memory. The patterns of rCBF response suggest that the areas identified are associated with limited capacity processes for encoding and retrieval.

Adult↗
PubMed1994

Cerebral responses to pain in patients with atypical facial pain measured by positron emission tomography.

The localised PET cerebral correlates of the painful experience in the normal human brain have previously been demonstrated. This study examined whether these responses are different in patients with chronic atypical facial pain. The regional cerebral responses to non-painful and painful thermal stimuli in six female patients with atypical facial pain and six matched female controls were studied by taking serial measurements of regional blood flow by PET. Both groups displayed highly significant differences in responses to painful heat compared with non-painful heat in the thalamus, anterior cingulate cortex (area 24), lentiform nucleus, insula, and prefrontal cortex. These structures are closely related to the "medial pain system". The atypical facial pain group had increased blood flow in the anterior cingulate cortex and decreased blood flow in the prefrontal cortex. These findings show the importance of the anterior cingulate cortex and the reciprocal (possibly inhibitory) connections with the prefrontal cortex in the processing of pain in patients with this disorder. A hypothesis is proposed to explain the mechanisms of cognitive and pharmacological manipulation of these pain processes.

Adult↗
PubMed1994

Reorganization of cortical blood flow and transcranial magnetic stimulation maps in human subjects after upper limb amputation.

1. Two complimentary techniques were used to study cortical function in six human upper limb amputees: positron emission tomographic (PET) measurements of regional cerebral blood flow (rCBF) were made in subjects during limb movements to study activation of the primary motor (M1), primary somatosensory (S1), and association cortices; and electromyographic responses to transcranial magnetic stimulation (TMS) were measured in proximal upper limb muscles to assess the excitability of corticospinal neurons in subjects at rest. 2. To explore possible cortical mechanisms governing the phantom limb phenomenon, PET and TMS findings were compared between subjects with acquired, traumatic upper limb amputations (n = 3), in whom phantom limb symptoms were prominent, and congenital upper limb amputees (n = 3) without phantom limbs. 3. Paced shoulder movements were associated with significant blood flow increases in the contralateral M1/S1 cortex of both groups of amputees. In traumatic amputees, these increases were present over a wider area and were of significantly greater magnitude in the partially deafferented cortex contralateral to the amputation. In congenital amputees blood flow increases were also present over a wider area in the partially deafferented M1/S1 cortex, but their magnitude was not significantly different from that in the normally afferented M1/S1 cortex. 4. Abnormal blood flow increases also were present in the partially deafferented M1/S1 cortex of traumatic amputees during movement of the ipsilateral, intact arm. Abnormal ipsilateral M1/S1 responses were not present during movement of the intact arm in the congenital group. 5. TMS studies showed that the abnormal blood flow increases in the partially deafferented M1 cortex of traumatic amputees were associated with increased corticospinal excitability.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗