Biomedical subjects

D H ffytche

Publications and source records attributed to D H ffytche.

10 recordsLinked to original sources

PubMed2003

Self-responsibility and the self-serving bias: an fMRI investigation of causal attributions.

We use causal attributions to infer the most likely cause of events in the social world. Internal attributions imply self-responsibility for events. The self-serving bias describes the tendency of normal subjects to attribute the causation of positive events internally ("I am responsible em leader ") and negative events externally ("Other people or situational factors are responsible em leader "). The self-serving bias has been assumed to serve a positive motivational function by enhancing self-esteem. Abnormalities of attributional style have been implicated in both depression and psychosis. We examined the neural basis of both self-responsibility and the self-serving bias using functional magnetic resonance imaging during the performance of attributional decision tasks. We found that the determination of self-responsibility recruits areas previously implicated in action simulation (bilateral premotor cortex and cerebellum), suggesting that such higher order social cognition is related to simpler internal models of goal-directed action. The dorsal striatum, previously implicated in motivated behavior, mediates the self-serving bias.

Adult↗

PubMed2003

fMRI BOLD response to increasing task difficulty during successful paired associates learning.

We used functional magnetic resonance imaging (fMRI) to assess cortical activations associated with increasing task difficulty (TD) in a visuospatial paired associates learning task. Encoding and retrieval were examined when 100% successful retrieval of three, four, or six object-location pairs had been attained (thus ensuring that performance was matched across subjects). As memory load increased, in general, the number of attempts taken to achieve 100% successful retrieval increased, while the number of trials correctly completed on the first attempt decreased. By modelling parametric variations in working memory load with BOLD signal changes we were able to identify brain regions displaying linear and nonlinear responses to increasing load. During encoding, load-independent activations were found in occipitoparietal cortices (excluding the precuneus for which linear load dependency was demonstrated), anterior cingulate, and cerebellum, while linear load-dependent activations in these same regions were found during retrieval. Nonlinear load-dependent responses, as identified by categorical contrasts between levels of load, were found in the right DLPFC and left inferior frontal gyrus. The cortical response to increasing cognitive demands or TD appears to involve the same, rather than an additional, network of brain regions "working harder."

Adult↗

PubMed2000

Imaging attentional and attributional bias: an fMRI approach to the paranoid delusion.

BACKGROUND: The pathophysiology of auditory hallucinations and delusions of control has been elucidated using functional imaging. Despite their clinical importance, there have been few similar attempts to investigate paranoid delusions. We have examined two components of social cognition (attentional and attributional biases) that contribute to the formation and maintenance of paranoid delusions, using functional magnetic resonance imaging (fMRI). METHOD: Normal subjects performed tasks requiring attentional and attributional judgements. We investigated the neural response particularly associated with attention to threatening material relevant to self and with the 'self-serving' attributional bias. RESULTS: The determination of relevance to self of verbal statements of differing emotional valence involved left ventrolateral prefrontal cortex (left inferior frontal gyrus, BA 47), right caudate and right cingulate gyrus (BA 24). Attention to threatening material relevant to self differentially activated a more dorsal region of the left inferior frontal gyrus (BA 44). Internal attributions of events, where the self was viewed as an active intentional agent, involved left precentral gyrus (BA 6) and left middle temporal gyrus (BA 39). Attribution of events in a non 'self-serving' manner required activation of the left precentral gyrus (BA 6). CONCLUSIONS: Anomalous activity or connectivity within these defined regions may account for the attentional or attributional biases subserving paranoid delusion formation. This provides a simple model for paranoid delusion formation that can be tested in patients.

Adult↗

PubMed2000

Human area V5 and motion in the ipsilateral visual field.

We have studied area V5 of the human brain with visually-evoked potential (VEP) and functional magnetic resonance imaging (fMRI) methods, using hemifield motion stimuli. Our results confirmed the presence of an ipsilateral field representation in V5 and found: (i) a delay in the ipsilateral response in V5, irrespective of the hemifield stimulated; (ii) a longer ipsilateral delay for left hemifield than for right hemifield stimulation; and (iii) in a patient with a section of the splenium, an absent ipsilateral response for right but not left hemifield stimulation. Together with neurophysiological and anatomical evidence in the monkey, our non-invasive spatial and temporal imaging studies in man reveal that ipsilateral V5 is activated by motion signals transferred from contralateral V5. The asymmetry of ipsilateral delay in normal subjects and the asymmetrical loss of ipsilateral response following splenial section imply that signals related to visual motion are transferred from one V5 to the other through two segregated pathways.

Adult↗

PubMed2000

Visual hallucinatory syndromes and the anatomy of the visual brain.

We have set out to identify phenomenological correlates of cerebral functional architecture within Charles Bonnet syndrome (CBS) hallucinations by looking for associations between specific hallucination categories. Thirty-four CBS patients were examined with a structured interview/questionnaire to establish the presence of 28 different pathological visual experiences. Associations between categories of pathological experience were investigated by an exploratory factor analysis. Twelve of the pathological experiences partitioned into three segregated syndromic clusters. The first cluster consisted of hallucinations of extended landscape scenes and small figures in costumes with hats; the second, hallucinations of grotesque, disembodied and distorted faces with prominent eyes and teeth; and the third, visual perseveration and delayed palinopsia. The three visual psycho-syndromes mirror the segregation of hierarchical visual pathways into streams and suggest a novel theoretical framework for future research into the pathophysiology of neuropsychiatric syndromes.

Aged↗

PubMed1999

fMRI and EEG responses to periodic visual stimulation.

EEG/VEP and fMRI responses to periodic visual stimulation are reported. The purpose of these experiments was to look for similar patterns in the time series produced by each method to help understand the relationship between the two. The stimulation protocol was the same for both sets of experiments and consisted of five complete cycles of checkerboard pattern reversal at 1.87 Hz for 30 s followed by 30 s of a stationary checkerboard. The fMRI data was analyzed using standard methods, while the EEG was analyzed with a new measurement of activation-the VEPEG. Both VEPEG and fMRI time series contain the fundamental frequency of the stimulus and quasi harmonic components-an unexplained double frequency commonly found in fMRI data. These results have prompted a reappraisal of the methods for analyzing fMRI data and have suggested a connection between our findings and much older published invasive electrophysiological measurements of blood flow and the partial pressures of oxygen and carbon dioxide. Overall our new analysis suggests that fMRI signals are strongly dependant on hydraulic blood flow effects. We distinguish three categories of fMRI signal corresponding to: focal activated regions of brain tissue; diffuse nonspecific regions of steal; and major cerebral vessels of arterial supply or venous drainage. Each category of signal has its own finger print in frequency, amplitude, and phase. Finally, we put forward the hypothesis that modulations in blood flow are not only the consequence but are also the cause of modulations in functional activity.

Adolescent↗

PubMed1999

The perceptual consequences of visual loss: 'positive' pathologies of vision.

Fifty patients with visual hallucinations and illusions secondary to degenerative eye disease reported remarkably stereotyped experiences. Questionnaire responses revealed five previously recognized categories of pathological vision (perseveration, illusory visual spread, polyopia, prosopometamorphopsia and micro/macropsia) and three novel categories (tessellopsia, hyperchromatopsia and dendropsia). Identical pathologies of vision occur in a range of clinical and experimental settings, suggesting that they reflect fundamental visual processes. The known neurophysiology of the visual cortex helps explain the phenomenology of the experiences and provides the basis for a neurobiologically based classification of positive and negative visual perceptual disorders.

Eye Diseases↗

PubMed1998

The functional anatomy of imagining and perceiving colour.

We report two functional magnetic resonance imaging experiments which reveal similarities and differences between perceptual and imaginal networks within the single visual submodality of colour. The first experiment contrasted viewing of a coloured and grey-scale Mondrian display, while the second contrasted a relative colour judgement with a spatial task and required the generation of mental images. Our results show that colour perception activates the posterior fusiform gyrus bilaterally (area V4), plus right-sided anterior fusiform and lingual gyri, striate cortex (area V1), and the left and right insula. Colour imagery activated right anterior fusiform gyrus, left insula, right hippocampus and parahippocampal gyrus, but not V4 or V1. The findings reconcile neurological case studies suggesting a double dissociation between deficits in colour imagery and perception and point to anterior fusiform, parahippocampal gyri and hippocampus as the location for stored representations of coloured objects.

Brain Mapping↗

PubMed1996

Motion specific responses from a blind hemifield.

In a previous study we showed that fast moving stimuli activate V5, an area specialized for motion, at very short latencies through a pathway that reaches it without passing through V1. Using the same technique of visual evoked responses, we have tested our conclusions by studying patient GY, whose V1 is damaged but whose V5 is intact. In spite of the contralateral hemi-blindness due to his V1 lesion, GY has a residual visual capacity that allows him to perceive, consciously, fast but not slow moving stimuli presented in his affected hemifield. By stimulating GY's 'blind' hemifield and comparing the responses with those obtained from normal subjects, we were able to study the relative contribution of V1 and V5 to the visual evoked response to motion in normal subjects. We found that GY's early response to fast motion is preserved and correlates with activity elicited in control subjects over area V5, while slow motion, pattern offset, and pattern reversal stimuli failed to elicit responses in GY. The results confirm our previous conclusions: namely, that the early part of the motion evoked response is generated in area V5 and that signals reach this area through a dynamically parallel pathway that bypasses area V1. They go on to demonstrate that neurophysiological activity in the prestriate cortex correlates with the conscious visual perception of motion.

Adult↗

PubMed1995

The parallel visual motion inputs into areas V1 and V5 of human cerebral cortex.

Published clinical evidence has led us to hypothesize that there are parallel pathways which lead to the striate (V1) and prestriate cortex in the human brain. We have used the technique of visually evoked EEG coupled to magnetoencephalography (MEG) to test our hypothesis, by detecting the timing of arrival of signals into these visual areas, using published PET evidence to guide us in the location of the evoked response sources. We found that, if the moving stimulus has a speed of 22 degrees s-1, signals arrive in V5 before V1; with speeds of < 6 degrees s-1, signals arrive in V1 first. We conclude that, in addition to the classical picture of a sequential input to prestriate cortex through V1, there is also a fast parallel input which by-passes V1. The parallelism manifests itself only as a function of the characteristics of the visual stimulus, a phenomenon we describe as dynamic parallelism. The results obtained help us explain the residual motion vision of patients with lesions in V1 or V5.

Afferent Pathways↗