Biomedical subjects

M J Brammer

Publications and source records attributed to M J Brammer.

At least 19 recordsLinked to original sources

PubMed2001

Depersonalization disorder: thinking without feeling.

Patients with depersonalization disorder (DP) experience a detachment from their own senses and surrounding events, as if they were outside observers. A particularly common symptom is emotional detachment from the surroundings. Using functional magnetic resonance imaging (fMRI), we compared neural responses to emotionally salient stimuli in DP patients, and in psychiatric and healthy control subjects. Six patients with DP, 10 with obsessive-compulsive disorder (OCD), and six volunteers were scanned whilst viewing standardized pictures of aversive and neutral scenes, matched for visual complexity. Pictures were then rated for emotional content. Both control groups rated aversive pictures as much more emotive, and demonstrated in response to these scenes significantly greater activation in regions important for disgust perception, the insula and occipito-temporal cortex, than DP patients (covarying for age, years of education and total extent of brain activation). In DP patients, aversive scenes activated the right ventral prefrontal cortex. The insula was activated only by neutral scenes in this group. Our findings indicate that a core phenomenon of depersonalization--absent subjective experience of emotion--is associated with reduced neural responses in emotion-sensitive regions, and increased responses in regions associated with emotion regulation.

Adult↗

PubMed2001

An fMRI study of reduced left prefrontal activation in schizophrenia during normal inhibitory function.

Functional magnetic resonance imaging (fMRI) was used to investigate the hypothesis that schizophrenia is associated with a dysfunction of prefrontal brain regions during motor response inhibition. Generic brain activation of six male medicated patients with schizophrenia was compared to that of seven healthy comparison subjects matched for sex, age, and education level while performing 'stop' and 'go-no-go' tasks. No group differences were observed in task performance. Patients, however, showed reduced BOLD signal response in left anterior cingulate during both inhibition tasks and reduced left rostral dorsolateral prefrontal and increased thalamus and putamen BOLD signal response during stop task performance. Despite good task performance, patients with schizophrenia thus showed abnormal neural network patterns of reduced left prefrontal activation and increased subcortical activation when challenged with motor response inhibition.

Adult↗

PubMed2001

Differential activation of temporal cortex during sentence completion in schizophrenic patients with and without formal thought disorder.

The neural correlates of processing linguistic context in schizophrenic patients with formal thought disorder (FTD) were examined. Six right-handed male patients with prominent 'positive' FTD were compared with six schizophrenic patients without FTD and seven volunteers, matched for cognitive and demographic variables. Functional magnetic resonance imaging (IMRI) was used to measure cerebral activation while subjects read and completed sentence stems out loud. During a GENERATION condition, subjects were required to generate a word which completed the sentence stem appropriately. During a DECISION condition, subjects selected and articulated one of two presented terminal words. A READING condition served as baseline. The three conditions were compared with each other. Regions activated were identified in each group, and between-group differences were detected using an ANCOVA. When GENERATION was compared with READING, FTD patients showed less activation in the right superior temporal gyrus than patients without FTD or controls, but greater activation in the left inferior frontal, inferior temporal and fusiform gyri. FTD patients also showed an attenuated right temporal response when GENERATION was compared with DECISION. This differential engagement of the right temporal cortex was independent of differences in the speed or accuracy of responses, whereas the left fronto-temporal differences in activation were not evident after covarying for task errors. The attenuated engagement of right temporal cortex, which is implicated in language comprehension at the discourse level, is consistent with neuropsychological evidence linking thought disorder with deficits in processing linguistic context.

Acute Disease↗

PubMed2001

Dispersed activation in the left temporal cortex for speech-reading in congenitally deaf people.

Does the lateral temporal cortex require acoustic exposure in order to become specialized for speech processing? Six hearing participants and six congenitally deaf participants, all with spoken English as their first langugage, were scanned using functional magnetic resonance imaging while performing a simple speech-reading task. Focal activation of the left lateral temporal cortex was significantly reduced in the deaf group compared with the hearing group. Activation within this region was present in individual deaf participants, but varied in location from person to person. Early acoustic experience may be required for regions within the left temporal cortex in order to develop into a coherent network with subareas devoted to specific speech analysis functions.

Adult↗

PubMed2001

Audio-visual speech perception in schizophrenia: an fMRI study.

Abnormalities in the integration of auditory and visual language inputs could underlie many core psychotic features. Perceptual confusion may arise because of the normal propensity of visual speech perception to evoke auditory percepts. Recent functional neuroimaging studies of normal subjects have demonstrated activation in auditory-linguistic brain areas in response to silent lip-reading. Three functional magnetic resonance imaging experiments were carried out on seven normal volunteers, and 14 schizophrenia patients, half of whom were actively psychotic. The tasks involved listening to auditory speech, silent lip-reading (visual speech), and perception of meaningless lip movements (visual non-speech). Subjects also undertook a behavioural study of audio-visual word identification designed to evoke perceptual fusions. Patients and controls both showed susceptibility to audio-visual fusions on the behavioural task. The patient group as a whole showed less activation relative to controls in superior and inferior posterior temporal areas while performing the silent lip-reading task. Attending to visual non-speech, the patients activated less posterior (occipito-temporal) and more anterior (frontal, insular and striatal) brain areas than controls. This difference was accounted for largely by the psychotic subgroup. Insular and striatal areas were also activated in both subject groups in the auditory speech perception condition, thus demonstrating the bimodal sensitivity of these regions. The results suggest that schizophrenia patients with psychotic symptoms respond to visually ambiguous stimuli (non-speech) by activation of polysensory structures. This could reflect particular processing strategies and may increase susceptibility to certain paranoid and hallucinatory symptoms.

Adult↗

PubMed2001

Neural correlates of formal thought disorder in schizophrenia: preliminary findings from a functional magnetic resonance imaging study.

BACKGROUND: Formal thought disorder (FTD) is a core symptom of schizophrenia, but its pathophysiology is little understood. We examined the neural correlates of FTD using functional magnetic resonance imaging. METHODS: Blood oxygenation level-dependent contrast was measured using functional magnetic resonance imaging while 6 patients with schizophrenia and 6 control subjects spoke about 7 Rorschach inkblots for 3 minutes each. In patients, varying degrees of thought-disordered speech were elicited during each "run." In a within-subject design, the severity of positive FTD was correlated with the level of blood oxygenation level-dependent contrast in the 2 runs that showed the highest variance of FTD in each patient. RESULTS: The severity of positive FTD in patients was negatively correlated (P<.001) with signal changes in the left superior and middle temporal gyri. Positive correlations were evident in the cerebellar vermis, the right caudate body, and the precentral gyrus. CONCLUSIONS: The severity of positive FTD was inversely correlated with the level of activity in the Wernicke area, a region implicated in the production of coherent speech. Reduced activity in this area might contribute to the articulation of incoherent speech. Because of the small sample size, these findings should be considered preliminary.

Adult↗

PubMed2001

Time courses of left and right amygdalar responses to fearful facial expressions.

Despite the many studies highlighting the role of the amygdala in fear perception, few have examined differences between right and left amygdalar responses. Using functional magnetic resonance imaging (fMRI), we examined neural responses in three groups of healthy volunteers (n = 18) to alternating blocks of fearful and neutral faces. Initial observation of extracted time series of both amygdalae to these stimuli indicated more rapid decreases of right than left amygdalar responses to fearful faces, and increasing magnitudes of right amygdalar responses to neutral faces with time. We compared right and left responses statistically by modeling each time series with (1) a stationary fit model (assuming a constant magnitude of amygdalar response to consecutive blocks of fearful faces) and (2) an adaptive model (no assumptions). Areas of significant sustained nonstationarity (time series points with significantly greater adaptive than stationary model fits) were demonstrated for both amygdalae. There was more significant nonstationarity of right than left amygdalar responses to neutral, and left than right amygdalar responses to fearful faces. These findings indicate significant variability over time of both right and left amygdalar responses to fearful and neutral facial expressions and are the first demonstration of specific differences in time courses of right and left amygdalar responses to these stimuli.

Adult↗

PubMed2001

Mapping motor inhibition: conjunctive brain activations across different versions of go/no-go and stop tasks.

Conjunction analysis methods were used in functional magnetic resonance imaging to investigate brain regions commonly activated in subjects performing different versions of go/no-go and stop tasks, differing in probability of inhibitory signals and/or contrast conditions. Generic brain activation maps highlighted brain regions commonly activated in (a) two different go/no-go task versions, (b) three different stop task versions, and (c) all 5 inhibition task versions. Comparison between the generic activation maps of stop and go/no-go task versions revealed inhibitory mechanisms specific to go/no-go or stop task performance in 15 healthy, right-handed, male adults. In the go/no-go task a motor response had to be selectively executed or inhibited in either 50% or 30% of trials. In the stop task, the motor response to a go-stimulus had to be retracted on either 50 or 30% of trials, indicated by a stop signal, shortly (250 ms) following the go-stimulus. The shared "inhibitory" neurocognitive network by all inhibition tasks comprised mesial, medial, and inferior frontal and parietal cortices. Generic activation of the go/no-go task versions identified bilateral, but more predominantly left hemispheric mesial, medial, and inferior frontal and parietal cortices. Common activation to all stop task versions was in predominantly right hemispheric anterior cingulate, supplementary motor area, inferior prefrontal, and parietal cortices. On direct comparison between generic stop and go/no-go activation maps increased BOLD signal was observed in left hemispheric dorsolateral prefrontal, medial, and parietal cortices during the go/no-go task, presumably reflecting a left frontoparietal specialization for response selection.

Adult↗

PubMed2001

Detection of audio-visual integration sites in humans by application of electrophysiological criteria to the BOLD effect.

Electrophysiological studies in nonhuman primates and other mammals have shown that sensory cues from different modalities that appear at the same time and in the same location can increase the firing rate of multisensory cells in the superior colliculus to a level exceeding that predicted by summing the responses to the unimodal inputs. In contrast, spatially disparate multisensory cues can induce a profound response depression. We have previously demonstrated using functional magnetic resonance imaging (fMRI) that similar indices of crossmodal facilitation and inhibition are detectable in human cortex when subjects listen to speech while viewing visually congruent and incongruent lip and mouth movements. Here, we have used fMRI to investigate whether similar BOLD signal changes are observable during the crossmodal integration of nonspeech auditory and visual stimuli, matched or mismatched solely on the basis of their temporal synchrony, and if so, whether these crossmodal effects occur in similar brain areas as those identified during the integration of audio-visual speech. Subjects were exposed to synchronous and asynchronous auditory (white noise bursts) and visual (B/W alternating checkerboard) stimuli and to each modality in isolation. Synchronous and asynchronous bimodal inputs produced superadditive BOLD response enhancement and response depression across a large network of polysensory areas. The most highly significant of these crossmodal gains and decrements were observed in the superior colliculi. Other regions exhibiting these crossmodal interactions included cortex within the superior temporal sulcus, intraparietal sulcus, insula, and several foci in the frontal lobe, including within the superior and ventromedial frontal gyri. These data demonstrate the efficacy of using an analytic approach informed by electrophysiology to identify multisensory integration sites in humans and suggest that the particular network of brain areas implicated in these crossmodal integrative processes are dependent on the nature of the correspondence between the different sensory inputs (e.g. space, time, and/or form).

Adult↗

PubMed2001

Arousal dissociates amygdala and hippocampal fear responses: evidence from simultaneous fMRI and skin conductance recording.

The experience and appraisal of threat is essential to human and animal survival. Lesion evidence suggests that the subjective experience of fear relies upon amygdala-medial frontal activity (as well as autonomic arousal), whereas the factual context of threat stimuli depends upon hippocampal-lateral frontal activity. This amygdala-hippocampus dissociation has not previously been demonstrated in vivo. To explore this differentiation, we employed functional magnetic resonance imaging (fMRI) and simultaneous skin conductance response (SCR) measures of phasic arousal, while subjects viewed fearful versus neutral faces. fMRI activity was subaveraged according to whether or not the subject evoked an arousal SCR to each discrete face stimulus. The fMRI-with arousal and fMRI-without arousal data provided a distinct differentiation of amygdala and hippocampal networks. Amygdala-medial frontal activity was observed only with SCRs, whereas hippocampus-lateral frontal activity occurred only in the absence of SCRs. The findings provide direct evidence for a dissociation between human amygdala and hippocampus networks in the visceral experience versus declarative fact processing of fear.

Adult↗

PubMed2001

Differential frontal activation in schizophrenia and bipolar illness during verbal fluency.

INTRODUCTION: The precise nature of frontal lobe dysfunction in schizophrenia remains unclear. We have previously demonstrated, using fMRI, a task-specific attenuation of frontal activation in schizophrenic patients. By using an identical methodology in matched bipolar subjects, we sought to determine whether this finding is specific to schizophrenia or a correlate of psychosis in general. METHOD: Five dextral male bipolar patients and matching groups of schizophrenic subjects and controls were studied using fMRI. Echoplanar images were acquired while subjects performed two paced tasks: covert verbal fluency and a semantic decision task. Generic brain activation maps were constructed from individual images by sinusoidal regression analysis. Between-group differences in the mean power of experimental response were identified on a voxel-wise basis by an analysis of variance (ANOVA). RESULTS: The bipolar patients showed extensive prefrontal activation during verbal fluency which was significantly greater than in controls. There was no difference in the prefrontal BOLD response during the semantic decision task. CONCLUSIONS: These data indicate that bipolar patients show a strikingly different pattern of frontal responses compared to those with schizophrenia and provide further evidence that abnormal frontal activation in psychotic disorders is more apparent during verbal fluency than semantic decision.

Adult↗

PubMed2001

Cortical substrates for the perception of face actions: an fMRI study of the specificity of activation for seen speech and for meaningless lower-face acts (gurning).

Can the cortical substrates for the perception of face actions be distinguished when the superficial visual qualities of these actions are very similar? Two fMRI experiments are reported. Compared with watching the face at rest, observing silent speech was associated with bilateral activation in a number of temporal cortical regions, including the superior temporal sulcus (STS). Watching face movements of similar extent and duration, but which could not be construed as speech (gurning; Experiment 1b) was not associated with activation of superior temporal cortex to the same extent, especially in the left hemisphere. Instead, the peak focus of the largest cluster of activation was in the posterior part of the inferior temporal gyrus (right, BA 37). Observing silent speech, but not gurning faces, was also associated with bilateral activation of inferior frontal cortex (BA 44 and 45). In a second study, speechreading and observing gurning faces were compared within a single experiment, using stimuli which comprised the speaker's face and torso (and hence a much smaller image of the speaker's face and facial actions). There was again differential engagement of superior temporal cortex which followed the pattern of Experiment 1. These findings suggest that superior temporal gyrus and neighbouring regions are activated bilaterally when subjects view face actions--at different scales--that can be interpreted as speech. This circuitry is not accessed to the same extent by visually similar, but linguistically meaningless actions. However, some temporal regions, such as the posterior part of the right superior temporal sulcus, appear to be common processing sites for processing both seen speech and gurns.

Adult↗

PubMed2001

A functional study of auditory verbal imagery.

BACKGROUND: We used functional MRI to examine the functional anatomy of inner speech and different forms of auditory verbal imagery (imagining speech) in normal volunteers. We hypothesized that generating inner speech and auditory verbal imagery would be associated with left inferior frontal activation, and that generating auditory verbal imagery would involve additional activation in the lateral temporal cortices. METHODS: Subjects were scanned, while performing inner speech and auditory verbal imagery tasks, using a 1.5 Tesla magnet. RESULTS: The generation of inner speech was associated with activation in the left inferior frontal/insula region, the left temporo-parietal cortex, right cerebellum and the supplementary motor area. Auditory verbal imagery in general, as indexed by the three imagery tasks combined, was associated with activation in the areas engaged during the inner speech task, plus the left precentral and superior temporal gyri (STG), and the right homologues of all these areas. CONCLUSIONS: These results are consistent with the use of the 'articulatory loop' during both inner speech and auditory verbal imagery, and the greater engagement of verbal self-monitoring during auditory verbal imagery.

Adult↗

PubMed2001

Modality specific neural correlates of auditory and somatic hallucinations.

Somatic hallucinations occur in schizophrenia and other psychotic disorders, although auditory hallucinations are more common. Although the neural correlates of auditory hallucinations have been described in several neuroimaging studies, little is known of the pathophysiology of somatic hallucinations. Functional magnetic resonance imaging (fMRI) was used to compare the distribution of brain activity during somatic and auditory verbal hallucinations, occurring at different times in a 36 year old man with schizophrenia. Somatic hallucinations were associated with activation in the primary somatosensory and posterior parietal cortex, areas that normally mediate tactile perception. Auditory hallucinations were associated with activation in the middle and superior temporal cortex, areas involved in processing external speech. Hallucinations in a given modality seem to involve areas that normally process sensory information in that modality.

Adult↗

PubMed2000

Lexical retrieval during fluent speech production: an fMRI study.

We investigated the neural correlates of lexical retrieval during fluent speech production using fMRI. Blood oxygenation level dependent (BOLD) contrast was measured while subjects spoke about 7 Rorschach inkblots for 3 min each. Varying degrees of speech rate were elicited during each run. In a within-subject design, the number of words produced was correlated with the BOLD contrast in the two runs in each subject that showed the highest variance of speech output. The rate of articulation was positively correlated with activation in the left superior temporal (BA 22) and supramarginal (BA 39/ 40) gyri. The main negative correlations were in the fusiform gyri bilaterally (BA 19), the posterior cingulate (BA 30) and superior occipital gyrus (BA 19). Lexical retrieval during continuous language production engages areas in the left temporal and inferior parietal cortex. This pattern of activation differs from that evident during the generation of single words (verbal fluency), which is more associated with left prefrontal activation.

Adult↗

PubMed2000

The neural correlates of orienting: an integration of fMRI and skin conductance orienting.

In fMRI studies, the averaging of neural activity across multiple trials might obscure important psychophysiological subprocesses. The orienting response (OR) is a distinctive subprocess signalling the active orientation of attention towards potentially significant events. We sought to elucidate fMRI activity associated with visual stimuli that did or did not evoke simultaneously recorded electrodermal ORs (using customised skin conductance recording). 'With-OR' stimuli were associated with significant activity in the hippocampus, anterior cingulate and ventromedial prefrontal cortex. Averaged analysis revealed activity only in the expected visual circuits. Our results suggest that potentially significant stimuli (with-OR) activate different functional networks to familiar (without-OR) stimuli, and that orienting may therefore be an informative subprocess to consider in cognitive fMRI studies.

Attention↗

PubMed2000

Silent speechreading in the absence of scanner noise: an event-related fMRI study.

In a previous study we used functional magnetic resonance imaging (fMRI) to demonstrate activation in auditory cortex during silent speechreading. Since image acquisition during fMRI generates acoustic noise, this pattern of activation could have reflected an interaction between background scanner noise and the visual lip-read stimuli. In this study we employed an event-related fMRI design which allowed us to measure activation during speechreading in the absence of acoustic scanner noise. In the experimental condition, hearing subjects were required to speechread random numbers from a silent speaker. In the control condition subjects watched a static image of the same speaker with mouth closed and were required to subvocally count an intermittent visual cue. A single volume of images was collected to coincide with the estimated peak of the blood oxygen level dependent (BOLD) response to these stimuli across multiple baseline and experimental trials. Silent speechreading led to greater activation in lateral temporal cortex relative to the control condition. This indicates that activation of auditory areas during silent speechreading is not a function of acoustic scanner noise and confirms that silent speechreading engages similar regions of auditory cortex as listening to speech.

Adult↗

PubMed2000

Evidence from functional magnetic resonance imaging of crossmodal binding in the human heteromodal cortex.

BACKGROUND: Integrating information from the different senses markedly enhances the detection and identification of external stimuli. Compared with unimodal inputs, semantically and/or spatially congruent multisensory cues speed discrimination and improve reaction times. Discordant inputs have the opposite effect, reducing performance and slowing responses. These behavioural features of crossmodal processing appear to have parallels in the response properties of multisensory cells in the superior colliculi and cerebral cortex of non-human mammals. Although spatially concordant multisensory inputs can produce a dramatic, often multiplicative, increase in cellular activity, spatially disparate cues tend to induce a profound response depression. RESULTS: Using functional magnetic resonance imaging (fMRI), we investigated whether similar indices of crossmodal integration are detectable in human cerebral cortex, and for the synthesis of complex inputs relating to stimulus identity. Ten human subjects were exposed to varying epochs of semantically congruent and incongruent audio-visual speech and to each modality in isolation. Brain activations to matched and mismatched audio-visual inputs were contrasted with the combined response to both unimodal conditions. This strategy identified an area of heteromodal cortex in the left superior temporal sulcus that exhibited significant supra-additive response enhancement to matched audio-visual inputs and a corresponding sub-additive response to mismatched inputs. CONCLUSIONS: The data provide fMRI evidence of crossmodal binding by convergence in the human heteromodal cortex. They further suggest that response enhancement and depression may be a general property of multisensory integration operating at different levels of the neuroaxis and irrespective of the purpose for which sensory inputs are combined.

Acoustic Stimulation↗