1,721,220 research outputs found
Can the neuropsychological case-study approach be applied to schizophrenia?
No full textNeuropsychological studies of schizophrenia typically apply a small number of tests to a large group of patients. This approach has at least two drawbacks. First, the heterogeneity of the condition will lead to group means which may not reflect the behaviour of any individual. Secondly, it is difficult to infer the nature of the underlying cognitive impairments from a small number of tests, since good performance on a particular test depends on many different cognitive processes. In these circumstances it is more appropriate to apply the methods of cognitive neuropsychology where a large number of tests are used on a single case. This approach has proved fruitful in the study of neurological patients. We have intensively studied 5 chronic schizophrenic patients. These patients varied greatly in terms of overall ability. However, all patients, whatever their overall ability, performed badly on tests sensitive to frontal lobe lesions. This result suggests impairment of the supervisory attentional system in these patients. In addition, one patient suffered from a visual agnosia
The origins of forgetting in a case of isolated retrograde amnesia following a haemorrhage: evidence from functional imaging
No full textFollowing a left superior dorsolateral prefrontal haemorrhage, a man in his 40s presented with a dense isolated retrograde amnesia for 19 years preceding the stroke. This period of his life contained many highly stressful situations. Functional neuroimaging using PET was carried out while he attempted to recall events using family snapshots as stimuli. There were three conditions - those where the stimuli related to the amnesic period and in which he had been present at the event (amnesic-present condition), analogous events from outside that period (non-amnesic present condition) and events where he was not present (not-present condition). Activation in the amnesic-present condition differed significantly from the other two conditions in three cortical regions. Activation was greater in part of the precuneus, but less in both the right posterior ventrolateral frontal cortex and in a region close to the lesion. We argue that an explanation in terms of malingering can be rejected and instead propose that this deficit can be explained by the fact that the recursive self-cueing of memory traces characteristic of autobiographical retrieval was not properly triggered
Comment on "Wandering minds: The default network and stimulus-independent thought"
No full textMason et al. (Reports, 19 January 2007, p. 393) attributed activity in certain regions of the "resting" brain to the occurrence of mind-wandering. However, previous research has demonstrated the difficulty of distinguishing this type of stimulus-independent thought from stimulus-oriented thought (e.g., watchfulness). Consideration of both possibilities is required to resolve this ambiguity
Brain activity during memory retrieval: The influence of imagery and semantic cueing
Full text linkThe effects of imagery and semantic relatedness on cued retrieval of word pairs were examined in a functional imaging study of healthy volunteers. Subjects underwent 12 PET scans, preceded by the paced presentation of 12 paired associates. The associates were dichotomized into imageable and non-imageable groups. Within each group, the strength of semantic association between members of pairs was varied in an ordinal fashion. Subsequently, neural activity was measured while subjects were cued with the first item of each pair and required to recall the associated word. Recall of imageable words, when compared with non-imageable ones, was associated with activation of the precuneus, consistent with our hypothesis that this region is important in visual imagery at episodic retrieval. The reverse comparison, non-imageable versus imageable recall, was associated with activation of the left dorsolateral prefrontal cortex. Within both imageable and non-imageable groups, decreasing semantic association showed a corresponding increase in frontal activity bilaterally. One possible explanation is that of a practice-related effect, weaker-linked pairs having a greater number of pre-scan presentations. However this explanation is incomplete as the most semantically distant, and most rehearsed, pairs (randomly linked) were associated with a reversal of this effect. This finding can be explained if frontal activity is associated with the difficulty of eliminating inappropriate responses at retrieval. For both randomly linked pairs and closely related pairs it is more likely that erroneous responses will be generated and, therefore, the work done to eliminate them will be greater Our findings indicate that patterns of neural activity during cued recall depend upon the nature of the material and on the degree of association between the cue and the response
CEREBRAL REPRESENTATIONS FOR EGOCENTRIC SPACE: FUNCTIONAL-ANATOMICAL EVIDENCE FROM CALORIC VESTIBULAR STIMULATION AND NECK VIBRATION
No full text"Hey John": Signals conveying communicative intention toward the self activate brain regions associated with "mentalizing," regardless of modality
No full textSuccessful communication between two people depends first on the recognition of the intention to communicate. Such intentions may be conveyed by signals directed at the self, such as calling a person's name or making eye contact. In this study we use functional magnetic resonance imaging to show that the perception of these two signals, which differ in modality and sensory channel, activate common brain regions: the paracingulate cortex and temporal poles bilaterally. These regions are part of a network that has been consistently activated when people are asked to think about the mental states of others. Activation of this network is independent of arousal as measured by changes in pupil diameter
Is multivariate analysis of PET data more revealing than the univariate approach? Evidence from a study of episodic memory retrieval
Full text linkIn a functional imaging study of cued paired associate retrieval, in which the strength of association between pair members was systematically varied, we predicted increased right frontal activity as a function of weakening semantic linkage. An initial univariate analysis found the opposite effect, with greater right frontal activity during recall of strongly linked paired associates, This unexpected result led us to perform a multivariate analysis of covariance (MANCOVA),an approach which proved more informative, This analysis showed that the most significant source of task-related variance was accounted for by a nonlinear relationship not predicted by the prior hypothesis and not revealed by the standard univariate approach
Identification of the central vestibular projections in man: a positron emission tomography activation study.
No full textThe 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
Brain systems for encoding and retrieval of auditory - Verbal memory. An in vivo study in humans
No full textLong-term auditory-verbal memory comprises, at a neuropsycho logical level, a number of distinct cognitive processes. In the present study we determined the brain systems engaged during encoding (experiment I) and retrieval (experiment 2) of episodic auditory-verbal material. In the separate experiments, PET measurements of regional cerebral blood flow (rCBF), an index of neural activity, were performed in normal volunteers during either the encoding or the retrieval of paired word associates. In experiment I, a dual task interference paradigm was used to isolate areas involved in episodic encoding from those which would be concurrently activated by other cognitive processes associated with the presentation of paired associates, notably priming. In experiment 2, we used the cued retrieval of paired associates from episodic or from semantic memory in order to isolate the neural correlates of episodic memories. Encoding of episodic memory was associated with activation of the left prefrontal cortex and the retrosplenial area of the cingulate cortex, while retrieval from episodic memory was associated with activation of the precuneus bilaterally and of the right prefrontal cortex. These results are compatible with the patterns of activation reported in a previous PET memory experiment in which encoding and retrieval were studied concurrently. They also indicate that separate brain systems are engaged during the encoding and retrieval phases of episodic auditory-verbal memory. Retrieval from episodic memory engages a different, but overlapping, system to that engaged by retrieval from semantic memory, a finding that lends functional anatomical support to this neuro-psychological distinction. © 1995 Oxford University Press
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