Showing papers by "Raymond J. Dolan published in 1995"
TL;DR: The localisation of brain regions involved in normal attribution of mental states and contextual problem solving is feasible and may have implication for the neural basis of autism.
1,432 citations
TL;DR: Memory-related imagery was associated with significant activation of a medial parietal area, the precuneus, which provides strong evidence that it is a key part of the neural substate of visual imagery occurring in conscious memory recall.
653 citations
TL;DR: This article found that episodic memory was associated with activation of the left prefrontal cortex and the retrosplenial area of the cingulate cortex, while retrieval from episodic recall was also associated with the precuneus bilaterally and of the right prefrontal cortex.
Abstract: Long-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.
463 citations
TL;DR: Chronic schizophrenic patients can show a normal magnitude of frontal activation when matched for performance with controls, and they fail to show the expected reductions of activity in the superior temporal cortex, which may reflect abnormal functional connectivity between frontal and temporal cortex.
Abstract: BACKGROUND This study examined the pattern of cerebral blood flow observed in chronic schizophrenic patients while they performed a paced verbal fluency task. Such tasks engage a distributed brain system associated with willed action. Since willed action is impaired in many chronic schizophrenic patients we hypothesised that task performance would be associated with an abnormal pattern of blood flow.
METHOD Positron emission tomography (PET) was applied to 18 chronic schizophrenic patients stratified into three groups on the basis of verbal fluency performance and current symptoms. Regional cerebral blood flow (rCBF) was measured while the patients performed (a) verbal fluency, (b) word categorisation, and (c) word repetition. Results were compared with six normal controls matched for age, sex and premorbid IQ. Analysis was restricted to six brain regions previously identified in studies of normal volunteers.
RESULTS In five brain areas, including the left dorsolateral prefrontal cortex, the patients showed the same pattern of activation as control subjects. However, in the left superior temporal cortex, all patient groups failed to show the normal decrease in blood flow when verbal fluency was compared with word repetition.
CONCLUSION These observations suggest that (a) chronic schizophrenic patients can show a normal magnitude of frontal activation when matched for performance with controls, and (b) they fail to show the expected reductions of activity in the superior temporal cortex. This latter result may reflect abnormal functional connectivity between frontal and temporal cortex.
420 citations
TL;DR: PET data provide in vivo evidence that an impaired cognitive-task-induced activation of the anterior cingulate cortex in schizophrenic patients can be significantly modulated by a dopaminergic manipulation.
Abstract: DOPAMINERGIC dysregulation remains an empirical cornerstone for theories concerning the causation of schizophrenia. Evidence for a dopamine system dysfunction in schizophrenia includes the psychosis-inducing effects of dopaminergic agonists1,2 and the antipsychotic potency of dopaminergic antagonists3,4. Here we use positron emission tomography (PET) to examine the regulatory role of dopamine on cortical function in normal subjects and unmedicated schizophrenic patients. Using a factorial experimental design, we compared the effect of dopaminergic manipulation with apomorphine on a neural response to a cognitive task. In the schizophrenic patients, relative to controls, an impaired cognitive activation of the anterior cingulate cortex was significantly modulated by a manipulation of dopaminergic neurotransmission. Thus, after apomorphine, the schizophrenic subjects displayed a significantly enhanced cognitive activation of the anterior cingulate cortex relative to the controls. These data provide in vivo evidence that an impaired cognitive-task-induced activation of the anterior cingulate cortex in schizophrenic patients can be significantly modulated by a dopaminergic manipulation.
378 citations
TL;DR: Recovery from depression is associated with increases in r CBF in the same areas in which focal decreases in rCBF are described in the depressed state in comparison with normal controls.
Abstract: We have previously described focal abnormalities of regional cerebral blood flow (rCBF) in the left dorsolateral prefrontal cortex (DLPFC), anterior cingulate cortex and angular gyrus in 40 patients with major depression. We now report on the patterns of change in rCBF in a subgroup of 25 of the same patients who were rescanned following clinical remission of depression. Fifteen patients were scanned when optimally matched for drug treatment (4) or drug free on both occasions (11). The other 10 patients were fully recovered but could not be matched for drug status for clinical and ethical reasons. In a paired comparison of the same patients when ill and following recovery it was evident that remission was associated with a significant increase in rCBF in the left DLPFC and medial prefrontal cortex including anterior cingulate. Increases in rCBF in the angular gyrus were not seen when the comparison of depressed and recovered scans was matched for medication. The previously described relationship between clinical symptoms and brain perfusion in the depressed state was no longer present in the recovered state; this supports the hypothesis of state relatedness. Thus, recovery from depression is associated with increases in rCBF in the same areas in which focal decreases in rCBF are described in the depressed state in comparison with normal controls.
345 citations
TL;DR: The results suggest that the presence of chorea per se may not be determined by alterations in striatal dopamine receptor binding, but that rigidity in Huntington's disease is associated with severe striatal D1 and D2 receptor loss.
Abstract: We have used PET to study striatal D1 and D2 receptor binding in 10 patients with either the choreic or akinetic-rigid variants of Huntington's disease and in three patients with other causes of chorea. Background rigidity and bradykinesia in choreic patients were scored with a four-point scale. PET studies showed a severe and parallel reduction of both striatal D1 and D2 receptor binding in Huntington's disease patients irrespective of their predominant phenotype (mean reduction 60%). Huntington's disease patients with rigidity showed more pronounced reduction of striatal D1 and D2 binding compared with those without rigidity. A case of chorea associated with systemic lupus erythematosus had normal D2 binding. These results suggest that the presence of chorea per se may not be determined by alterations in striatal dopamine receptor binding, but that rigidity in Huntington's disease is associated with severe striatal D1 and D2 receptor loss.
155 citations
01 Jan 1995
TL;DR: The results of this study indicate that separate brain systems are engaged during the encoding and retrieval phases of episodic auditory-verbal memory, and engage a different, but overlapping, system to that engaged by retrieval from semantic memory.
Abstract: Long-term auditory-verbal memory comprises, at a neuropsychological level, a number of distinct cognitive processes. In the present study we determined the brain systems engaged during encoding (experiment 1) 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 1, 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 neuropsychological distinction.
112 citations
TL;DR: The data suggest that acute blockade of cholinergic neurotransmission affects diverse brain areas, including components of the visual and motor systems, and, in addition, modulates memory task activations at distinct points in a distributed network for memory function.
Abstract: Scopolamine, a muscarinic antagonist, impairs memory performance in both humans and animals. In this study, repeated measurements of regional cerebral blood flow (rCBF) were made in normal volunteers whilst performing auditory verbal memory tasks, before and after the administration of scopolamine (0.4 mg s.c.) or placebo. Compared to placebo, scopolamine increased blood flow in the lateral occipital cortex bilaterally and the left orbitofrontal region. Scopolamine decreased rCBF in the region of the right thalamus, the precuneus and the right and left lateral premotor areas. Scopolamine attenuated memory-task-induced increases of rCBF in the left and right prefrontal cortex and the right anterior cingulate region. These data suggest that acute blockade of cholinergic neurotransmission affects diverse brain areas, including components of the visual and motor systems, and, in addition, modulates memory task activations at distinct points in a distributed network for memory function.
61 citations
TL;DR: A review of recent work using Positron Emission Tomography to examine brain systems involved in auditory-verbal memory is presented, addressing sub-components of memory such as the use of visual imagery as a mnemonic strategy and the functional anatomical evidence for the episodic/semantic memory distinction.
Abstract: A review of recent work using Positron Emission Tomography (PET) to examine brain systems involved in auditory-verbal memory is presented. Initial work delineated widespread brain regions which were, to a large extent, in agreement with existing neuropsychological literature. Expanding on this, a number of studies have examined memory encoding and retrieval separately. Additionally, experiments have been carried out to specifically address sub-components of memory such as the use of visual imagery as a mnemonic strategy, the functional anatomical evidence for the episodic/semantic memory distinction and the different brain regions involved in explicit and implicit memory tasks.
35 citations
TL;DR: The neurobiology of the psychoses has been a controversial issue and functional imaging techniques now provide a powerful tool to address critical questions concerning their fundamental nature.