Biomedical subjects

C D Frith

Publications and source records attributed to C D Frith.

At least 91 records · Page 5Linked to original sources

PubMed1998

A neuromodulatory role for the human amygdala in processing emotional facial expressions.

Localized amygdalar lesions in humans produce deficits in the recognition of fearful facial expressions. We used functional neuroimaging to test two hypotheses: (i) that the amygdala and some of its functionally connected structures mediate specific neural responses to fearful expressions; (ii) that the early visual processing of emotional faces can be influenced by amygdalar activity. Normal subjects were scanned using PET while they performed a gender discrimination task involving static grey-scale images of faces expressing varying degrees of fear or happiness. In support of the first hypothesis, enhanced activity in the left amygdala, left pulvinar, left anterior insula and bilateral anterior cingulate gyri was observed during the processing of fearful faces. Evidence consistent with the second hypothesis was obtained by a demonstration that amygdalar responses predict expression-specific neural activity in extrastriate cortex.

Adult↗

PubMed1998

The functional roles of prefrontal cortex in episodic memory. II. Retrieval.

Functional neuroimaging studies of memory retrieval show consistent activation of the right prefrontal and superior parietal cortex. We examined the specific role of the prefrontal cortex during retrieval with the hypothesis that this region mediates monitoring processes necessary for optimal recall. During functional neuroimaging with PET, subjects retrieved verbal material under two conditions. In the first, an organizational structure had been provided, prior to scanning, and this formed the basis for a monitored memory search while the scan took place. A comparison condition did not require a monitored search because recall was externally cued. In both conditions, when compared with baseline tasks prefrontal cortex and medial parietal activation was observed. Within the right prefrontal cortex activation an anatomical dissociation was seen between the dorsal and ventral prefrontal cortex. The dorsal region showed greater activation when monitoring demands were emphasized, while the ventral region showed greater activation when external cueing was emphasized. An unpredicted dissociation within the superior parietal activation was also observed, a dorsal region showing activation during the monitored search task and a more ventral region showing activation under the externally cued condition. The results provide evidence for functional specialization of the right prefrontal cortex for discrete cognitive processes during episodic memory retrieval.

Adult↗

PubMed1998

The functional anatomy of attention to visual motion. A functional MRI study.

Attention can enhance or modulate neural responses to stimuli at early and late stages of sensory processing. We were interested in the modulatory effect of attention to visual motion on cortical responses as measured by functional MRI. Subjects were scanned during repeated presentations of identical stimuli (visual motion) while only the attentional component of the task was varied. Enhanced haemodynamic responses during attentive conditions defined an occipitoparietofrontal system, including sensory and association areas, as well as the medial thalamus and superior colliculus. Attentional modulation was not restricted to extrastriate areas (including V3a and the V5 complex) but was also evident, to a lesser degree, in early visual areas close to the calcarine fissure (V1/V2 border). Attention-related enhancement of cortical responsiveness is discussed in terms of data that implicate modulatory short-term changes in synaptic efficacy and reciprocal connections between striate, extrastriate, parietal and frontal areas. Given the similarity of our attentional network to that controlling eye movements, the results of this study are in accord with theories linking oculomotor control and attention.

Attention↗

PubMed1998

Knowing where things are parahippocampal involvement in encoding object locations in virtual large-scale space.

The involvement of the medial temporal-lobe region in allocentric mapping of the environment has been observed in human lesion and functional imaging work. Cognitive models of environmental learning ascribe a key role to salient landmarks in representing large-scale space. In the present experiments we examined the neural substrates of the topographical memory acquisition process when environmental landmarks were more specifically identifiable. Using positron emission tomography (PET), we measured regional cerebral blood flow changes while normal subjects explored and learned in a virtual reality environment. One experiment involved an environment containing salient objects and textures that could be used to discriminate different rooms. Another experiment involved a plain empty environment in which rooms were distinguishable only by their shape. Learning in both cases activated a network of bilateral occipital, medial parietal, and occipitotemporal regions. The presence of salient objects and textures in an environment additionally resulted in increased activity in the right parahippocampal gyrus. This region was not activated during exploration of the empty environment. These findings suggest that encoding of salient objects into a representation of large-scale space is a critical factor in instigating parahippocampal involvement in topographical memory formation in humans and accords with previous studies implicating parahippocampal areas in the encoding of object location.

Adult↗

PubMed1998

Pathophysiology of 'positive' thought disorder in schizophrenia.

BACKGROUND: Formal thought disorder is a characteristic feature of psychosis, but little is known of its pathophysiology. We have investigated this in schizophrenia using positron emission tomography (PET). METHOD: Regional cerebral blood flow was measured using H2(15)O and PET while six people with schizophrenia were describing a series of 12 ambiguous pictures which elicited different degrees of thought-disordered speech. In a within-subject design, the severity of 'positive' thought disorder was correlated with cerebral blood flow across the 12 scans in each subject. RESULTS: Verbal disorganisation (positive thought disorder) was inversely correlated with activity in the inferior frontal, cingulate and left superior temporal cortex, and positively correlated with activity in the parahippocampal/anterior fusiform region bilaterally, and in the body of the right caudate (P < 0.001). The total amount of speech produced (independent of thought disorder) was positively correlated with activity in the left inferior frontal and left superior temporal cortex. CONCLUSIONS: The severity of positive thought disorder was inversely correlated with activity in areas implicated in the regulation and monitoring of speech production. Reduced activity in these regions may contribute to the articulation of the linguistic anomalies that characterise positive thought disorder. The positive correlations between positive thought disorder and parahippocampal/anterior fusiform activity may reflect this region's role in the processing of linguistic anomalies.

Adult↗

PubMed1998

A framework for assessing communication in mental illness.

Many studies support the notion of semantic and/or pragmatic difficulties in people with mental illness. This paper describes a framework (based on a discourse analysis model) for the assessment and reassessment of communication in mentally ill persons.

Communication Disorders↗

PubMed1998

'Confabulation' in narrative discourse by schizophrenic patients.

There are many clinical reports of confabulation by schizophrenic patients. This study provides evidence of a form of confabulation by schizophrenic patients in tasks which do not include a memory component. It uses a linguistic framework to analyse the components of this confabulation.

Cognition Disorders↗

PubMed1997

Modulating irrelevant motion perception by varying attentional load in an unrelated task.

Lavie's theory of attention proposes that the processing load in a relevant task determines the extent to which irrelevant distractors are processed. This theory was tested by asking participants in a study to perform linguistic tasks of low or high load while ignoring irrelevant visual motion in the periphery of the display. Although task and distractor were unrelated, both functional imaging of motion-related activity in cortical area V5 and psychophysical measures of the motion aftereffect showed reduced motion processing during high load in the linguistic task. These findings fulfill the prediction that perception of irrelevant distractors depends on the relevant processing load.

Adult↗

PubMed1997

Recalling routes around london: activation of the right hippocampus in taxi drivers.

Functional imaging to date has examined the neural basis of knowledge of spatial layouts of large-scale environments typically in the context of episodic memory with specific spatiotemporal references. Much human behavior, however, takes place in very familiar environments in which knowledge of spatial layouts has entered the domain of general facts often referred to as semantic memory. In this study, positron emission tomography (PET) was used to examine the neural substrates of topographical memory retrieval in licensed London taxi drivers of many years experience while they recalled complex routes around the city. Compared with baseline and other nontopographical memory tasks, this resulted in activation of a network of brain regions, including the right hippocampus. Recall of famous landmarks for which subjects had no knowledge of their location within a spatial framework activated similar regions, except for the right hippocampus. This suggests that the hippocampus is involved in the processing of spatial layouts established over long time courses. The involvement of similar brain areas in routes and landmarks memory indicates that the topographical memory system may be primed to respond to any relevant topographical stimulation; however, the right hippocampus is recruited specifically for navigation in large-scale spatial environments. In contrast, nontopographical semantic memory retrieval involved the left inferior frontal gyrus, with no change in activity in medial temporal regions.

Adult↗

PubMed1997

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

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.

Adult↗

PubMed1997

The appreciation of visual jokes in people with schizophrenia: a study of 'mentalizing' ability.

It has been suggested that certain characteristic symptoms of schizophrenia reflect a specific deficit in the ability to attribute mental states to others ('mentalizing'). Patients with negative features, particularly social withdrawal and blunted affect, those with thought disorder and patients with paranoid symptoms have difficulties when they try to infer what is going on in the minds of other people. This study examines this notion using two sets of cartoon jokes. While the first set can be understood purely using physical and semantic analysis, the second set requires that the viewer appreciates the mental state of the main character in order to 'get' the joke. For control subjects there was no difference in the ability to understand the two types of joke, while the schizophrenic patients found the mental state jokes significantly more difficult to understand. This effect was most marked in patients with behavioural disorders and those reporting passivity experiences. Those with paranoid delusions also showed a selective comprehension deficit with the mental state stimuli. Patients who were symptom free at the time of testing showed normal performance.

Adult↗

PubMed1997

Brain regions supporting intentional and incidental memory: a PET study.

Regional brain activity associated with intentional and incidental memory retrieval was studied with PET. Previously studied and new words were presented in either an intentional or an incidental memory task. Type of task was crossed with an encoding manipulation ('deep' vs 'shallow') which varied the probability that studied items would be remembered. In both tasks, deeply encoded items were associated with greater activation in the left hippocampus than were items that had received shallow encoding, suggesting that the involvement of the hippocampus in memory retrieval is independent of whether remembering is intentional or incidental. Right prefrontal and bilateral parietal cortex were more activated during the international task than during the incidental task, irrespective of encoding condition. Thus, these regions play a more extensive role in memory retrieval when remembering is intentional.

Brain↗

PubMed1997

Neural correlates of thinking in sign language.

Positron emission tomography (PET) was used to identify the brain regions activated during the 'inner signing' of sentences in subjects who were profoundly deaf and normally communicated using sign language. Although this appeared to involve the internal representation of hand and arm movements in space, it activated the left inferior frontal cortex rather than visuo-spatial areas. The activated region corresponds to that engaged during the silent articulation of sentences in hearing subjects. This suggests that 'inner signing' is mediated by similar regions to inner speech, and is consistent with neuropsychological data implicating the left hemisphere in the generation of sign language.

Adult↗

PubMed1997

Characterizing the relationship between BOLD contrast and regional cerebral blood flow measurements by varying the stimulus presentation rate.

This paper investigates the relationship between the blood oxygenation level dependent (BOLD) contrast effect and regional cerebral blood flow using the techniques of functional MRI (fMRI) and positron emission tomography (PET). A passive listening paradigm with parametric variation in word presentation rate was used to investigate the rate dependency of both BOLD contrast fMRI and H215O PET in primary auditory cortex. We attempted to equate the stimulus presentation acoustic environments by using prerecorded echoplanar imaging sounds during the PET paradigm. We show that there is a linear relationship between word presentation rate and cerebral blood flow in primary auditory cortex, whereas the relationship between BOLD contrast and stimulus presentation rate is highly nonlinear, showing a saturable effect. Two possible explanations for our results are discussed: a nonlinearity in the relationship between BOLD contrast and deoxyhemoglobin concentration or a nonlinear rate dependency of the physiological mechanisms causing changes in deoxyhemoglobin concentration.

Adult↗

PubMed1997

The functional anatomy of verbal initiation and suppression using the Hayling Test.

This study utilised positron emission tomography (PET) to identify the cortical areas involved in verbal initiation and suppression in normal subjects whilst performing a sentence completion test (the Hayling Test). In the first condition (response initiation) subjects were required to complete a sentence from which the last word was omitted, whereas in the second condition (response suppression) subjects were asked to complete a sentence with a word which made no sense in the context of the sentence. Subjects were also required to perform a control task in which they had to read out the last word of given sentences. Compared to the control task, response initiation was associated with left-sided activation of the frontal operculum, inferior frontal gyrus, middle temporal gyrus and the right anterior cingulate gyrus, whereas response suppression was associated with left frontal operculum, inferior frontal gyrus and right anterior cingulate gyrus activation. The difference in activation between the two conditions of the Hayling Test lay in the increased activation of the left middle temporal gyrus and the left inferior frontal gyrus during response initiation.

Adult↗

PubMed1997

Differential neural response to positive and negative feedback in planning and guessing tasks.

The neural mechanisms by which emotional and cognitive processing interact are unknown. Evidence from animal studies and neurological patients suggests that regions of the ventral striatum and orbitofrontal cortex, together with limbic structures such as the amygdala, are critical to such interactions. We used positron emission tomography to study the neural systems engaged by processing performance feedback under two conditions involving either a complex cognitive or a matched guessing task. The main activations associated with the processing of performance feedback under different task conditions involved foci in the medial caudate nucleus and the ventromedial orbitofrontal cortex. A differential modulation of these activations as a function of task type was observed. In particular the orbitofrontal activation associated with the presence of feedback was only seen in the guessing task. These data suggest that the ventral striatum and orbitofrontal cortex are involved in processing of feedback information, findings consistent with animal and neurological studies. We propose that differential activation associated with guessing compared to planning suggests enhanced neural processing of feedback when the outcome of a task is uncontrollable or when information must be assimilated across a number of trials to assess performance.

Adult↗

PubMed1997

The functional neuroanatomy of episodic memory.

Functional neuroimaging studies have revealed that effective encoding in episodic memory is associated with enhanced activity in left prefrontal cortex, whereas retrieval is accompanied by the enhancement of predominantly right-sided prefrontal activity. The extent of the contribution of prefrontal cortex to episodic memory, and the fact that the encoding and retrieval operations it supports are differentially lateralized, were unexpected on the basis of evidence from lesion studies. Such studies have highlighted the crucial role in episodic memory played by the hippocampus and related medial temporal lobe structures. Neuroimaging studies, however, have had only limited success in elucidating the role of the hippocampus in episodic memory. Refinements in experimental design and improved spatial resolution should promote rapid future progress with respect to this issue.

Brain↗

PubMed1997

The interaction between mood and cognitive function studied with PET.

BACKGROUND: Experimentally induced depressed mood is a suggested model for retarded depression. We describe the neural response associated with induced mood and the locus of the interaction between systems mediating mood and cognitive function. METHODS: Normal subjects performed a verbal fluency task during induced elated and depressed mood states. Regional cerebral blood flow (rCBF) was measured as an index of neural activity using Positron Emission Tomography (PET). RESULTS: In both elated and depressed mood state rCBF was increased in lateral orbitofrontal cortex, rCBF was also increased in the midbrain in elated mood. In the depressed condition rCBF was decreased in rostral medial prefrontal cortex. Verbal fluency produced an expected increase of rCBF in left dorsolateral prefrontal, inferior frontal and premotor cortex, anterior cingulate and insula cortex bilaterally, the left supramarginal gyrus posteriorly and the thalamus. Activation in the verbal fluency task was attenuated throughout the left prefrontal, premotor and cingulate cortex and thalamus in both elated and depressed mood conditions. An attenuation of anterior cingulate activation was specific to depressed mood. CONCLUSIONS: Alteration of mood is associated with activation of orbitofrontal cortex which may be critical to the experience of emotion. The mood induced modulation of verbal fluency induced activations is consistent with resting state findings of decreased function in these regions in depressed patients. The present data suggest that resting state rCBF profile may represent the modulation of spontaneous activity in this network by a core system that is dysfunctional in depression.

Adolescent↗