Orbitofrontal cortex is activated during breaches of expectation in tasks of visual attention.
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Adult↗
Biomedical subjects
C D Frith
Publications and source records attributed to C D Frith.
The functional neuroanatomy of comprehension and memory: the importance of prior knowledge.
Stories are a common way in which humans convey and acquire new information. Their effectiveness and memorability require that they be understood which, in turn, depends on two factors-whether the story makes sense and the prior knowledge that the listener brings to bear. Comprehension requires the linking of related pieces of information, some provided within the story and some by the listener, in a process establishing coherence. In this study, we examined brain activations associated with story processing. During PET scanning, passages of prose were read twice to subjects during successive scans with the requirement to remember them. These were either standard stories that were readily comprehensible, or unusual stories for which the global theme was very difficult to extract without prior knowledge of the mental framework. This was manipulated by the provision of relevant, irrelevant or no visual cues shortly before the story. Ratings of comprehension provided by the subjects just after each scan confirmed that standard stories were more comprehensible than the unusual stories, as were unusual stories with a mental framework compared with those without. PET results showed activation of anterior and ventral parts of the medial parietal/posterior cingulate cortex in association with hearing unusual stories when subjects were given prior knowledge of what it might be about. Medial ventral orbitofrontal cortex and left temporal pole activations were found to be associated with more general aspects of comprehension. Medial parietal cortex (precuneus) and left prefrontal cortex were associated with story repetition. We suggest that while the temporal pole is involved in the linking of propositions to build a narrative, the anterior medial parietal/posterior cingulate cortex is concerned with linking this information with prior knowledge. All of this occurs in the context of a general memory processing/retrieval system that includes the posterior parietal (precuneus) and prefrontal cortex. Knowledge of how distinct brain regions contribute differentially to aspects of comprehension and memory has implications for understanding how these processes break down in conditions of brain injury or disease.
Acoustic Stimulation↗
Explicit and implicit processing of words and pseudowords by adult developmental dyslexics: A search for Wernicke's Wortschatz?
Two groups of male university students who had been diagnosed as dyslexic when younger, and two groups of control subjects of similar age and IQ to the dyslexics, were scanned whilst reading aloud and during a task where reading was implicit. The dyslexics performed less well than their peers on a range of literacy tasks and were strikingly impaired on phonological tasks. In the reading aloud experiment, simple words and pseudowords were presented at a slow pace so that reading accuracy was equal for dyslexics and controls. Relative to rest, both normal and dyslexic groups activated the same peri- and extra-sylvian regions of the left hemisphere that are known to be involved in reading. However, the dyslexic readers showed less activation than controls in the left posterior inferior temporal cortex [Brodmann area (BA) 37, or Wernicke's Wortschatz], left cerebellum, left thalamus and medial extrastriate cortex. In the implicit reading experiment, word and pseudoword processing was contrasted to visually matched false fonts while subjects performed a feature detection paradigm. The dyslexic readers showed reduced activation in BA 37 relative to normals suggesting that this group difference, seen in both experiments, resides in highly automated aspects of the reading process. Since BA 37 has been implicated previously in modality-independent naming, the reduced activation may indicate a specific impairment in lexical retrieval. Interestingly, during the reading aloud experiment only, there was increased activation for the dyslexics relative to the controls in a pre-motor region of Broca's area (BA 6/44). We attribute this result to the enforced use of an effortful compensatory strategy involving sublexical assembly of articulatory routines. The results confirm previous findings that dyslexic readers process written stimuli atypically, based on abnormal functioning of the left hemisphere reading system. More specifically, we localize this deficit to the neural system underlying lexical retrieval.
Adult↗
The neural consequences of conflict between intention and the senses.
Normal sensorimotor states involve integration of intention, action and sensory feedback. An example is the congruence between motor intention and sensory experience (both proprioceptive and visual) when we move a limb through space. Such goal-directed action necessitates a mechanism that monitors sensorimotor inputs to ensure that motor outputs are congruent with current intentions. Monitoring in this sense is usually implicit and automatic but becomes conscious whenever there is a mismatch between expected and realized sensorimotor states. To investigate how the latter type of monitoring is achieved we conducted three fully factorial functional neuroimaging experiments using PET measures of relative regional cerebral blood flow with healthy volunteers. In the first experiment subjects were asked to perform Luria's bimanual co-ordination task which involves either in-phase (conditions 1 and 3) or out-of-phase (conditions 2 and 4) bimanual movements (factor one), while looking towards their left hand. In half of the conditions (conditions 3 and 4) a mirror was used that altered visual feedback (factor two) by replacing their left hand with the mirror image of their right hand. Hence (in the critical condition 4) subjects saw in-phase movements despite performing out-of-phase movements. This mismatch between intention, proprioception and visual feedback engendered cognitive conflict. The main effect of out-of-phase movements was associated with increased neural activity in posterior parietal cortex (PPC) bilaterally [Brodmann area (BA) 40, extending into BA 7] and dorsolateral prefrontal cortex (DLPFC) bilaterally (BA 9/46). The main effect of the mirror showed increased neural activity in right DLPFC (BA 9/ 46) and right superior PPC (BA 7) only. Analysis of the critical interaction revealed that the mismatch condition led to a specific activation in the right DLPFC alone (BA 9/46). Study 2, using an identical experimental set-up but manipulating visual feedback from the right hand (instead of the left), subsequently demonstrated that this right DLPFC activation was independent of the hand attended. Finally, study 3 removed the motor intentional component by moving the subjects' hand passively, thus engendering a mismatch between proprioception and vision only. Activation in the right lateral prefrontal cortex was now more ventral than in studies 1 or 2 (BA 44/45). A direct comparison of studies 1 and 3 (which both manipulated visual feedback from the left hand) confirmed that a ventral right lateral prefrontal region is primarily activated by discrepancies between signals from sensory systems, while a more dorsal area in right lateral prefrontal cortex is activated when actions must be maintained in the face of a conflict between intention and sensory outcome.
Adult↗
Dissociable neural responses to facial expressions of sadness and anger.
Previous neuroimaging and neuropsychological studies have investigated the neural substrates which mediate responses to fearful, disgusted and happy expressions. No previous studies have investigated the neural substrates which mediate responses to sad and angry expressions. Using functional neuroimaging, we tested two hypotheses. First, we tested whether the amygdala has a neural response to sad and/or angry facial expressions. Secondly, we tested whether the orbitofrontal cortex has a specific neural response to angry facial expressions. Volunteer subjects were scanned, using PET, while they performed a sex discrimination task involving static grey-scale images of faces expressing varying degrees of sadness and anger. We found that increasing intensity of sad facial expression was associated with enhanced activity in the left amygdala and right temporal pole. In addition, we found that increasing intensity of angry facial expression was associated with enhanced activity in the orbitofrontal and anterior cingulate cortex. We found no support for the suggestion that angry expressions generate a signal in the amygdala. The results provide evidence for dissociable, but interlocking, systems for the processing of distinct categories of negative facial expression.
Adult↗
Abnormal neural integration related to cognition in schizophrenia.
A striking feature of schizophrenia is the diversity of the phenomenology both within and between patients. This diversity can be contrasted with the well-circumscribed and stable deficits seen in classic neuropsychological syndromes. The argument will be advanced that the classic lesion model, based on the notion of a segregated deficit, is inappropriate in schizophrenia. Instead the idea will be developed that a more appropriate model is one derived from concepts of neural integration across large-scale brain networks. Empirical data derived from positron emission tomography (PET) within our laboratory that provide support for this suggestion will be presented. One critical observation from these data is a disruption of prefrontal-temporal interactions, under a variety of cognitive activation paradigms, in both chronic medicated and acute unmedicated schizophrenic patients. Furthermore, these data indicate that both regional and interregional neuronal function, including prefrontal-temporal interactions, can be significantly modulated by a neurochemical perturbation of ascending dopaminergic systems. The latter observations suggest that the deficit of abnormal cortico-cortical interactions are to some extent modifiable by neuromodulatory neurotransmitter systems.
Acute Disease↗
Spatio-temporal prediction modulates the perception of self-produced stimuli.
We investigated why self-produced tactile stimulation is perceived as less intense than the same stimulus produced externally. A tactile stimulus on the palm of the right hand was either externally produced, by a robot or self-produced by the subject. In the conditions in which the tactile stimulus was self-produced, subjects moved the arm of a robot with their left hand to produce the tactile stimulus on their right hand via a second robot. Subjects were asked to rate intensity of the tactile sensation and consistently rated self-produced tactile stimuli as less tickly, intense, and pleasant than externally produced tactile stimuli. Using this robotic setup we were able to manipulate the correspondence between the action of the subjects' left hand and the tactile stimulus on their right hand. First, we parametrically varied the delay between the movement of the left hand and the resultant movement of the tactile stimulus on the right hand. Second, we implemented varying degrees of trajectory perturbation and varied the direction of the tactile stimulus movement as a function of the direction of left-hand movement. The tickliness rating increased significantly with increasing delay and trajectory perturbation. This suggests that self-produced movements attenuate the resultant tactile sensation and that a necessary requirement of this attenuation is that the tactile stimulus and its causal motor command correspond in time and space. We propose that the extent to which self-produced tactile sensation is attenuated (i.e., its tickliness) is proportional to the error between the sensory feedback predicted by an internal forward model of the motor system and the actual sensory feedback produced by the movement.
Adult↗
A specific role for the thalamus in mediating the interaction of attention and arousal in humans.
The physiological basis for the interaction of selective attention and arousal is not clearly understood. Here we present evidence in humans that specifically implicates the thalamus in this interaction. We used functional magnetic resonance imaging to measure brain activity during the performance of an attentional task under different levels of arousal. Activity evoked in the ventrolateral thalamus by the attentional task changed as a function of arousal. The highest level of attention-related thalamic activity is seen under conditions of low arousal (secondary to sleep deprivation) compared with high arousal (secondary to caffeine administration). Other brain regions were also active during the attentional task, but these areas did not change their activity as a function of arousal. Control experiments establish that this pattern of changes in thalamic activity cannot be accounted for by nonspecific effects of arousal on cerebral hemodynamics. We conclude that the thalamus is involved in mediating the interaction of attention and arousal in humans.
Adult↗
How do we select perceptions and actions? Human brain imaging studies.
The selective nature of human perception and action implies a modulatory interaction between sensorimotor processes and attentional processes. This paper explores the use of functional imaging in humans to explore the mechanisms of perceptual selection and the fate of irrelevant stimuli that are not selected. Experiments with positron emission tomography show that two qualitatively different patterns of modulation of cerebral blood flow can be observed in experiments where non-spatial visual attention and auditory attention are manipulated. These patterns of modulation of cerebral blood flow modulation can be described as gain control and bias signal mechanisms. In visual and auditory cortex, the dominant change in cerebral blood flow associated with attention to either modality is related to a bias signal. The relation of these patterns of modulation to attentional effects that have been observed in single neurons is discussed. The existence of mechanisms for selective perception raises the more general question of whether irrelevant ignored stimuli are nevertheless perceived. Lavie's theory of attention proposes that the degree to which ignored stimuli are processed varies depending on the perceptual load of the current task. Evidence from behavioural and functional magnetic resonance imaging studies of ignored visual motion processing is presented in support of this proposal.
Attention↗
Knowing where and getting there: a human navigation network.
The neural basis of navigation by humans was investigated with functional neuroimaging of brain activity during navigation in a familiar, yet complex virtual reality town. Activation of the right hippocampus was strongly associated with knowing accurately where places were located and navigating accurately between them. Getting to those places quickly was strongly associated with activation of the right caudate nucleus. These two right-side brain structures function in the context of associated activity in right inferior parietal and bilateral medial parietal regions that support egocentric movement through the virtual town, and activity in other left-side regions (hippocampus, frontal cortex) probably involved in nonspatial aspects of navigation. These findings outline a network of brain areas that support navigation in humans and link the functions of these regions to physiological observations in other mammals.
Brain Mapping↗
Brain activations in schizophrenia during a graded memory task studied with functional neuroimaging.
BACKGROUND: Functional neuroimaging experiments have implicated prefrontal cortex (PFC) in memory processes. Several studies of schizophrenic patients have shown failure of activation in the dorsolateral region of PFC (DLPFC). We used a graded memory challenge to characterize functional neuroanatomical differences between schizophrenic and control subjects. The graded manipulation of task demands enabled us to assess group differences in the context of normal and abnormal psychological task performance. METHODS: Memory-related activity was assessed using positron emission tomography in schizophrenic patients and age-matched controls during performance of a graded memory task. Subjects underwent scanning while learning and recalling word lists of variable length. RESULTS: We used a model that assessed linear and nonlinear effects of memory load. Nonlinear group differences in DLPFC activation were observed. Controls showed a steepening slope of DLPFC increase as task demands increased. By contrast, schizophrenic subjects showed initial DLPFC increases that fell away with increasing memory load. The DLPFC response in schizophrenic subjects was closely related to measured task performance. In addition, schizophrenic subjects failed to show task-related decreases in activity in the left superior temporal and inferior parietal gyrus. CONCLUSIONS: Patients with schizophrenia showed a failure in DLPFC activation only in the face of diminished performance measures, suggesting that a full characterization of task-related changes in DLPFC activation must consider performance levels. However, striking failures of deactivation in superior temporal and inferior parietal regions were independent of task performance, possibly reflecting a core abnormality of the condition.
Adult↗
Differential activation of right superior parietal cortex and intraparietal sulcus by spatial and nonspatial attention.
Neuropsychological and functional neuroimaging studies have implicated the right posterior parietal cortex (PPC) in human spatial attention. We tested the hypothesis that this area is also involved in nonspatial aspects of attention and working memory using positron emission tomography in healthy volunteers. In an initial experiment, digits were presented in pseudo-random spatial locations, and subjects attended either to locations or digits in order to detect single targets (attention condition) or to sequences of stimuli (working memory (WM) condition). Right superior parietal cortex (BA7) and intraparietal sulcus (IPS) were active during both spatial (locations) and nonspatial (digits) tasks compared to rest, although more so for the former. Additionally, right PPC was activated to an even greater extent during tests of WM than of attention, especially for tests of spatial WM. There were no differences in activation of dorsolateral prefrontal cortex in the spatial versus nonspatial versions of the task, contrary to many previous studies. A follow-up experiment which presented abstract objects in a fixed, central location confirmed that right IPS was active during tests of nonspatial attention and also that this activation is not due to incidental spatial representation of digit stimuli. However, BA7 was not activated by this nonspatial, nondigit attentional task. Overall, these data suggest first that right IPS is recruited for both nonspatial and spatial attention and WM. Second, right BA7 is recruited specifically for spatial (both direct and indirect) forms of attentional processing. Finally, PPC activations in spatial WM tasks are likely to be due to a combination of spatial perception, attention, and WM, rather than to any of these individually.
Adult↗
Neural correlates of memory retrieval during recognition memory and cued recall.
Regional brain activity, measured by H215O PET, was investigated during recognition memory and word-stem cued recall of words in order to compare the neural correlates of two components of memory retrieval-effort and success-as a function of task. For each task there was a baseline and two retrieval conditions. In one retrieval condition (zero density), none of the test items corresponded to words encoded in a preceding study phase. Differences in activity between this condition and the baseline were employed to characterize the neural correlates of retrieval effort in each task. In the other retrieval condition (high density), 80% of the test items had been studied previously. Differences in brain activity between this condition and the zero-density condition were taken to represent the neural correlates of successful retrieval. The principal findings concern the right anterior prefrontal cortex, a region demonstrated previously to be active during episodic retrieval. Relative to baseline, this region showed no evidence of activation in the zero-density condition of the recognition task, but did show enhanced activity in the equivalent condition of the cued-recall task. In contrast, relative to the zero-density condition, the high-density condition was associated with increased right prefrontal activity during recognition, but reduced activity during cued recall. It is proposed that the right prefrontal cortex supports cognitive processes that operate on information retrieved in response to a test item and that these processes contribute to the evaluation of whether the information represents an appropriate prior episode.
Adult↗
Neural correlates of depth of processing effects on recollection: evidence from brain potentials and positron emission tomography.
The probability that words would be recollected during tests of recognition memory was varied by manipulating depth of processing at study. Experiment 1 employed scalp-recorded event-related potentials (ERPs), and identified as a correlate of recollection a late (onset c. 500 ms), strongly left-lateralized positive-going modulation of the ERP waveform. The findings from experiment 2, which employed positron emission tomography (PET), indicated that recollection was associated with activation of the left hippocampal formation together with an extensive region of left temporal and frontal cortex. The findings support current ideas about the role of the hippocampal formation in episodic memory retrieval, and provide complementary information about the time course and localization of the cortical correlates of the recollection of recently experienced words.
Behavior↗
How do we predict the consequences of our actions? A functional imaging study.
Humans are readily able to distinguish expected and unexpected sensory events. Whether a single mechanism underlies this ability is unknown. The most common type of expected sensory events are those generated as a consequence of self-generated actions. Using H2 15O PET, we studied brain responses to such predictable sensory events (tones) and to similar unpredictable events and especially how the processing of predictable sensory events is modified by the context of a causative self-generated action. Increases in activity when the tones were unpredictable were seen in the inferior and superior temporal lobe bilaterally, the right parahippocampal gyrus and right parietal cortex. Self-generated actions produced activity in a number of motor and premotor areas, including dorsolateral prefrontal cortex. We observed an interaction between the predictability of stimuli and self-generated actions in several areas, including the medial posterior cingulate cortex, left insula, dorsomedial thalamus, superior colliculus and right inferior temporal cortex. This modulation of activity associated with stimulus predictability in the context of self-generated actions implies that these areas may be involved in self-monitoring processes. Detection of expected stimuli and the detection of the sensory consequences of self-generated actions appear to be functionally distinct processes, and are carried out in different cortical areas. These observations support theoretical approaches to cognition that postulate the existence of a self-monitoring system.
Acoustic Stimulation↗
Monitoring for target objects: activation of right frontal and parietal cortices with increasing time on task.
The right prefrontal and parietal cortices have been implicated in attentional processing in both neuropsychological and functional neuroimaging literature. However, attention is a heterogeneous collection of processes, each of which may be underpinned by different neural networks. These attentional networks may interact, such that engaging one type of attentional process could influence the efficiency of another via overlapping neural substrates. We investigated the hypothesis that right frontal and parietal cortices provide the neuroanatomical location of the functional interaction between sustained attention and the process of selectively monitoring for target objects. Six healthy volunteers performed one of two tasks which required either selective or non-selective responding. The task lasted continuously for 18 min, during which time 3 Positron Emission Tomography (PET) scans were acquired for each task. This was repeated to obtain 12 PET measurements of regional cerebral blood flow (rCBF) for each subject. The right inferior frontal and parietal cortices were differentially activated by increasing time on task during the selective (S) vs non-selective (NS) task. Specifically, rCBF decreased with increasing time spent performing the NS task but not the S task. This result suggests that the normal deactivation in these areas as time on task increases is counteracted by the extra cognitive demands of selectively responding to target objects. Therefore, we have confirmed our hypothesis that right frontal and parietal cortices provide the neuroanatomical location for the modulation of object selection by sustained attention. We also identified the neuroanatomical correlates of each process separately, and confirmed earlier reports of prefrontal cortex and anterior cingulate activation associated with selective responding, and a fronto-parietal-thalamic network associated with sustained attention.
Adult↗
Theory of mind and psychoses.
BACKGROUND: A cardinal feature of schizophrenia is the sufferer's difficulty in interacting appropriately within the social milieu. This deficit has recently been associated with the concept of theory of mind, more commonly constructed as a working model to understand behavioural patterns in autistic children. In this paper the complex relationships between theory of mind, IQ and psychoses are addressed. METHODS: Five experimental groups were used; non-psychiatric controls, affective disorder, schizophrenia with normal pre-morbid IQ, schizophrenia with pre-morbid IQ in the mildly learning disabled range, and mild learning disability with no history of psychiatric illness. All subjects were given a first order Theory of Mind Task and if successful, a second order Theory of Mind Task was then administered. All subjects were rated using the Positive and Negative Symptom Scale (PANSS). RESULTS: Subjects with schizophrenia and subjects with mild learning disability show impaired ability on a second order theory of mind task. However, when patients who are unable to answer reality questions are removed from the analysis specific impairment of theory of mind is only seen in subjects with schizophrenia. Furthermore, this impairment is relatively specific to particular psychopathological clusters in subjects with schizophrenia. Even though the same clusters of psychopathology are also seen in patients with affective disorder, their presence is not associated with poor second order theory of mind performance. CONCLUSIONS: Impaired theory of mind on second order tests is specific to schizophrenia when compared to mild learning disability and affective disorder control groups. Subjects with schizophrenia and pre-morbid mild learning disability show greater impairment than subjects with schizophrenia and a pre-morbid IQ within the normal range.
Adult↗
Central cancellation of self-produced tickle sensation.
A self-produced tactile stimulus is perceived as less ticklish than the same stimulus generated externally. We used fMRI to examine neural responses when subjects experienced a tactile stimulus that was either self-produced or externally produced. More activity was found in somatosensory cortex when the stimulus was externally produced. In the cerebellum, less activity was associated with a movement that generated a tactile stimulus than with a movement that did not. This difference suggests that the cerebellum is involved in predicting the specific sensory consequences of movements, providing the signal that is used to cancel the sensory response to self-generated stimulation.
Adult↗