The role of the right hemisphere in the interpretation of figurative aspects of language. A positron emission tomography activation study

A PET investigation of the attribution of intentions with a nonverbal task

Several authors have demonstrated that theory of mind is associated with a cerebral pattern of activity involving the medial prefrontal cortex. This study was designed to determine the cerebral regions activated during attribution of intention to others, a task which requires theory-of-mind skills. Eight healthy subjects performed three nonverbal tasks using comic strips while PET scanning was performed. One condition required subjects to attribute intentions to the characters of the comic strips. The other two conditions involved only physical logic and knowledge about objects' properties: one condition involved characters, whereas the other only represented objects. The comparison of the attribution of intention condition with the physical logic with characters condition was associated with rCBF increases in the right middle and medial prefrontal cortex including Brodmann's area (BA) 9, the right inferior prefrontal cortex (BA 47), the right inferior temporal gyrus (BA 20), the left superior temporal gyrus (BA 38), the left cerebellum, the bilateral anterior cingulate, and the middle temporal gyri (BA 21). The comparison of the physical logic with characters condition and the physical logic without characters condition showed the activation of the lingual gyri (BA 17, 18, 19), the fusiform gyri (BA 37), the middle (BA 21) and superior (BA 22, 38) temporal gyri on both sides, and the posterior cingulate. These data suggest that attribution of intentions to others is associated with a complex cerebral activity involving the right medial prefrontal cortex when a nonverbal task is used. The laterality of this function is discussed.

Right and left hemisphere cooperation for drawing predictive and coherence inferences during normal story comprehension

In three experiments, healthy young participants listened to stories promoting inferences and named inference-related test words presented to the right visual field-Left Hemisphere (rvf-LH) or to the left visual field-Right Hemisphere (lvf-RH). Participants showed priming for predictive inferences only for target words presented to the lvf-RH; in contrast, they showed priming for coherence inferences only for target words presented to the rvf-LH. These results, plus the fact that patients with RH brain damage have difficulty drawing coherence inferences and do not show inference-related priming, suggest that information capable of supporting predictive inferences is more likely to be initially activated in the RH than the LH, but following coherence breaks these concepts (now coherence inferences) are completed in the LH. These results are consistent with the theory that the RH engages in relatively coarse semantic coding, which aids full comprehension of discourse.

Reading the mind in cartoons and stories: an fMRI study of 'theory of mind' in verbal and nonverbal tasks

Previous functional imaging studies have explored the brain regions activated by tasks requiring 'theory of mind'--the attribution of mental states. Tasks used have been primarily verbal, and it has been unclear to what extent different results have reflected different tasks, scanning techniques, or genuinely distinct regions of activation. Here we report results from a functional magnetic resonance imaging study (fMRI) involving two rather different tasks both designed to tap theory of mind. Brain activation during the theory of mind condition of a story task and a cartoon task showed considerable overlap, specifically in the medial prefrontal cortex (paracingulate cortex). These results are discussed in relation to the cognitive mechanisms underpinning our everyday ability to 'mind-read'.

Neurocognition of auditory sentence comprehension: event related fMRI reveals sensitivity to syntactic violations and task demands

The present study investigates the sensitivity of distinct brain regions to the syntactic processing of running speech. Experimental conditions varied the grammaticality of sentence types (correct vs. incorrect). Moreover, two different groups of subjects listened to the same sentence material, but followed two different task instructions. All participants were asked to listen to the auditory stimuli and to perform in a grammaticality judgment-task, whereas only half of the subjects were instructed to additionally repair incorrect sentences covertly. Significantly increased brain responses occurred in several left temporal areas as a function of sentences' grammaticality, particularly, in the 'pure' judgment-group. Spatial extent as well as the strength of focal brain activation changed as a function of grammaticality and task demand. A generally enhanced pattern of local blood supply to the right peri-sylvian cortex could be observed when individuals additionally realized the repair-task. In particular, the right inferior frontal gyrus (pars opercularis and pars triangularis) and the right temporal transverse gyrus (Heschl's gyrus) were more strongly affected by the repair-task demand. In contrast, an anterior portion of the superior temporal gyrus (planum polare) displayed increased activation bilaterally. Although left hemisphere activation varied clearly as a function of a sentence's grammaticality, the present findings demonstrate an involvement of the right peri-sylvian cortex, in particular, when task demands explicitly require an on-line repair. The results as a whole suggest a reconsideration of the notion that auditory language comprehension is restricted to the left hemisphere. The underlying mechanisms and the respective roles of both the left and the right hemisphere during speech processing are discussed.

Anatomical segregation of component processes in an inductive inference task

Inductive inference underlies much of human cognition. The essential component of induction is hypothesis selection based on some criterion of relevance. The purpose of this study was to determine the neural substrate of inductive inference, particularly hypothesis selection, using fMRI. Ten volunteers were shown stimuli consisting of novel animals under two task conditions, and asked to judge whether all the animals in the set were the same type of animal. In one condition, subjects were given a rule that specified the criteria for "same type of animal". In the other condition, subjects had to infer the rule without instruction. The two conditions were further factored into easy and difficult components. Rule inference was specifically associated with bilateral hippocampal activation while the task by difficulty interaction was associated with activation in right lateral orbital prefrontal cortex. We interpret the former in terms of semantic encoding of novel stimuli and the latter in terms of hypothesis selection. Thus, we show an anatomical dissociation between task implementation and task difficulty that may correspond to a critical psychological distinction in the processes necessary for inductive inference.

Imaging Cognition II: An Empirical Review of 275 PET and fMRI Studies

Positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have been extensively used to explore the functional neuroanatomy of cognitive functions. Here we review 275 PET and fMRI studies of attention (sustained, selective, Stroop, orientation, divided), perception (object, face, space/motion, smell), imagery (object, space/ motion), language (written/spoken word recognition, spoken/ no spoken response), working memory (verbal/numeric, object, spatial, problem solving), semantic memory retrieval (categorization, generation), episodic memory encoding (verbal, object, spatial), episodic memory retrieval (verbal, nonverbal, success, effort, mode, context), priming (perceptual, conceptual), and procedural memory (conditioning, motor, and nonmotor skill learning). To identify consistent activation patterns associated with these cognitive operations, data from 412 contrasts were summarized at the level of cortical Brodmann's areas, insula, thalamus, medial-temporal lobe (including hippocampus), basal ganglia, and cerebellum. For perception and imagery, activation patterns included primary and secondary regions in the dorsal and ventral pathways. For attention and working memory, activations were usually found in prefrontal and parietal regions. For language and semantic memory retrieval, typical regions included left prefrontal and temporal regions. For episodic memory encoding, consistently activated regions included left prefrontal and medial-temporal regions. For episodic memory retrieval, activation patterns included prefrontal, medial-temporal, and posterior midline regions. For priming, deactivations in prefrontal (conceptual) or extrastriate (perceptual) regions were consistently seen. For procedural memory, activations were found in motor as well as in non-motor brain areas. Analysis of regional activations across cognitive domains suggested that several brain regions, including the cerebellum, are engaged by a variety of cognitive challenges. These observations are discussed in relation to functional specialization as well as functional integration.

Imaging cognition II: An empirical review of 275 PET and fMRI studies

Positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have been extensively used to explore the functional neuroanatomy of cognitive functions. Here we review 275 PET and fMRI studies of attention (sustained, selective, Stroop, orientation, divided), perception (object, face, space/motion, smell), imagery (object, space/motion), language (written/spoken word recognition, spoken/no spoken response), working memory (verbal/numeric, object, spatial, problem solving), semantic memory retrieval (categorization, generation), episodic memory encoding (verbal, object, spatial), episodic memory retrieval (verbal, nonverbal, success, effort, mode, context), priming (perceptual, conceptual), and procedural memory (conditioning, motor, and nonmotor skill learning). To identify consistent activation patterns associated with these cognitive operations, data from 412 contrasts were summarized at the level of cortical Brodmann's areas, insula, thalamus, medial-temporal lobe (including hippocampus), basal ganglia, and cerebellum. For perception and imagery, activation patterns included primary and secondary regions in the dorsal and ventral pathways. For attention and working memory, activations were usually found in prefrontal and parietal regions. For language and semantic memory retrieval, typical regions included left prefrontal and temporal regions. For episodic memory encoding, consistently activated regions included left prefrontal and medial temporal regions. For episodic memory retrieval, activation patterns included prefrontal, medial temporal, and posterior midline regions. For priming, deactivations in prefrontal (conceptual) or extrastriate (perceptual) regions were consistently seen. For procedural memory, activations were found in motor as well as in non-motor brain areas. Analysis of regional activations across cognitive domains suggested that several brain regions, including the cerebellum, are engaged by a variety of cognitive challenges. These observations are discussed in relation to functional specialization as well as functional integration.

Distinct prefrontal activations in processing sequence at the sentence and script level: an fMRI study

Neuropsychological studies have shown that the prefrontal cortex is important in planning and monitoring everyday behaviour. In this study, using functional magnetic resonance imaging (fMRI), we investigated whether specific prefrontal regions are involved in processing a sequence of actions. Subjects were required to perform two different tasks: Script-event order and Sentence-word order. Script sequence and word sequence processing were found to activate partially overlapping areas which are known to be implicated in language processing. In addition, the Script-task activated a large area in the dorsolateral prefrontal cortex (Brodmann area 6 and 8, BA 6 and 8), in both the left and right hemispheres, as well as the left supplementary motor area and left angular gyrus (BA 39). Our results suggest that these prefrontal areas may be more specifically involved in the process of analysing sequential links in the action domain.

An event-related fMRI study of implicit phrase-level syntactic and semantic processing

Most neuroimaging studies of language function to date use a block-subtraction paradigm in which images acquired during relatively long periods of target stimuli are compared to those acquired during a control period. These studies typically require an overt response on the part of the subject, usually some type of discrimination or grammatical judgment by button press, or silent word generation. Results from studies of syntactic and semantic processing have generally been compatible with the classical correlation to Broca's area and Wernicke's area, respectively. Recently, functional magnetic resonance imaging (fMRI) studies departing from the block-subtraction paradigm in favor of event-related fMRI paradigms have been reported. We have extended the use of this approach to examine implicit (i.e., without an explicit task on the part of the subject) syntactic and semantic processing at the phrasal level, using visually presented verb phrases. Left BA 44 is more strongly activated for the syntactic condition than the semantic condition. BA 45, 10, and 46 show laterality differences: mostly left-lateralized for the syntactic condition and right-lateralized for the semantic condition. We also find activations of the inferior parietal lobe, consistent with a visual oddball response reported previously, and the anterior cingulate gyrus (BA 32), implicated for attention and memory-related processes in numerous studies.

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.

Form and content: dissociating syntax and semantics in sentence comprehension

The distinction between syntax (sentence form) and semantics (sentence meaning) is fundamental to our thinking about language. Whether and where this distinction is represented at the neural level is still a matter of considerable debate. In the present fMRI study, we examined the neural correlates of syntactic and semantic functions using an innovative activation paradigm specifically designed to unequivocally disentangle syntactic from lexicosemantic aspects of sentence processing. Our findings strongly indicate that a part of Broca's area (BA 44, pars opercularis) is critically implicated in processing syntactic information, whereas the lower portion of the left inferior frontal gyrus (BA 47, pars orbitalis) is selectively involved in processing the semantic aspects of a sentence.

The neuroimaging of long-term memory encoding processes

There needs to be more crosstalk between the lesion and functional neuroimaging memory literatures. This is illustrated by a discussion of episode and fact encoding. The lesion literature suggests several hypotheses about which brain regions underlie the storage of episode and fact information, which can be explored by functional neuroimaging. These hypotheses have been underexplored because neuroimaging studies of encoding have been insufficiently hypothesis-driven and have not controlled encoding-related processes sufficiently well to allow clear interpretations of results to be made. Nevertheless, there is good evidence that certain kinds of associative encoding and/or consolidation are sufficient to activate the medial temporal lobes, and preliminary evidence that some kinds of associative priming may reduce activation of this region. It remains to be proved that attentional orienting to certain kinds of novel information activates the medial temporal lobes. Evidence is growing that the HERA model, developed from neuroimaging rather than lesion data, requires modification and that frontal cortex encoding activations are probably caused by executive processes that are important in effortful memory processing. Neuroimaging studies allow the detection of encoding-related activations in previously unexpected brain regions (e.g. parietal lobes) and, in turn, these findings can be explored with lesion studies.

Activation of the right inferior frontal cortex during assessment of facial emotion

We measured regional cerebral blood flow (rCBF) using positron emission tomography (PET) to determine which brain regions are involved in the assessment of facial emotion. We asked right-handed normal subjects to assess the signalers' emotional state based on facial gestures and to assess the facial attractiveness, as well as to discriminate the background color of the facial stimuli, and compared the activity produced by each condition. The right inferior frontal cortex showed significant activation during the assessment of facial emotion in comparison with the other two tests. The activated area was located within a triangular area of the inferior frontal cortex in the right cerebral hemisphere. These results, together with those of previous imaging and clinical studies, suggest that the right inferior frontal cortex processes emotional communicative signals that could be visual or auditory and that there is a hemispheric asymmetry in the inferior frontal cortex in relation to the processing of emotional communicative signals.

Semantic integration in reading: engagement of the right hemisphere during discourse processing

We examined the brain areas involved in discourse processing by using functional MRI in 10 individuals as they read paragraphs, with or without a title, word by word for comprehension. Functional data were collected from 20 adjacent 5 mm axial slices. Discourse processing was associated with activation in inferior frontal and temporal regions of both cerebral hemispheres in the titled and untitled conditions. Moreover, there was substantially more right hemisphere activation for untitled than for the titled paragraphs. More specifically we found: (i) greater activation in the inferior temporal sulcus of both hemispheres for untitled than titled paragraphs; (ii) greater average volume of activation in response to untitled than titled paragraphs in the middle temporal sulcus of the right hemisphere and the reverse pattern in the left middle temporal sulcus. Consistent with previous studies of individuals with right hemisphere damage, we suggest that the right middle temporal regions may be especially important for integrative processes needed to achieve global coherence during discourse processing.

Neural pathways involved in the processing of concrete and abstract words

The purpose of this study was to delineate the neural pathways involved in processing concrete and abstract words using functional magnetic resonance imaging (fMRI). Word and pseudoword stimuli were presented visually, one at a time, and the participant was required to make a lexical decision. Lexical decision epochs alternated with a resting baseline. In each lexical decision epoch, the stimuli were either concrete words and pseudowords, or abstract words and pseudowords. Behavioral data indicated that, as with previous research, concrete word stimuli were processed more efficiently than abstract word stimuli. Analysis of the fMRI data indicated that processing of word stimuli, compared to the baseline condition, was associated with neural activation in the bilateral fusiform gyrus, anterior cingulate, left middle temporal gyrus, right posterior superior temporal gyrus, and left and right inferior frontal gyrus. A direct comparison between the abstract and concrete stimuli epochs yielded a significant area of activation in the right anterior temporal cortex. The results are consistent with recent positron emission tomography work showing right hemisphere activation during processing of abstract representations of language. The results are interpreted as support for a right hemisphere neural pathway in the processing of abstract word representations.

Medial temporal lobe activations in fMRI and PET studies of episodic encoding and retrieval

Early neuroimaging studies often failed to obtain evidence of medial temporal lobe (MTL) activation during episodic encoding or retrieval, but a growing number of studies using functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) have provided such evidence. We review data from fMRI studies that converge on the conclusion that posterior MTL is associated with episodic encoding; too few fMRI studies of retrieval have reported MTL activations to allow firm conclusions about their exact locations. We then turn to a recent meta-analysis of PET studies (Lepage et al., Hippocampus 1998;8:313-322) that appears to contradict the fMRI encoding data. Based on their analysis of the rostrocaudal distribution of activations reported during episodic encoding or retrieval, Lepage et al. (1998) concluded that anterior MTL is strongly associated with episodic encoding, whereas posterior MTL is strongly associated with episodic retrieval. After considering the evidence reviewed by Lepage et al. (1998) along with additional studies, we conclude that PET studies of encoding reveal both anterior and posterior MTL activations. These observations indicate that the contradiction between fMRI and PET studies of encoding was more apparent than real. However, PET studies have reported anterior MTL encoding activations more frequently than have fMRI studies. We consider possible sources of these differences.

Autonoetic awareness, executive social skills, and the appreciation of intention: figurative reasoning in amnesia, confabulation, and schizophrenia

This paper presents a cognitive neuropsychological model of the appreciation of unfamiliar abstract speech. The model elaborates upon the proposals of Bottini et al. (1994) by suggesting that we come to appreciate unfamiliar metaphorical speech in the autonoetically aware state. The specific executive skills of (1) an "as if" processor (2) a shared relevance seeker and monitor are harnessed to retrieval of information from personal long-term memory or imagination. The same cognitive system is assumed to handle other forms of indirect speech which need disambiguation as well as situations in which the intention or belief state of another has to be inferred. Predictions concerning the behavioural consequences of malfunctions occurring at different stages within the system are set out.

METHOD

To illustrate the behavioural consequences of differential system dysfunction, data collected from four case studies are presented. Each case performed two tasks. These entailed the appreciation of true/false functional sentences and unfamiliar metaphors. The sentences both required the need to reason analogically and were matched for syntactic complexity and number of words.

RESULTS

Clear similarities were seen in the performance of the new metaphors test between a patient with Korsakoff syndrome and consequent amnesia and one with negative feature schizophrenia. The same test also highlights similar processing deficits in a case of Korsakoff syndrome with amnesia and confabulation and a schizophrenic patient with formal thought disorder. By proposing different loci for system malfunctions within and across diagnoses the characteristic clinical and/or cognitive features of the illnesses or syndromes are addressed. The importance of recognising the implications of specific cognitive dysfunctions across diagnoses for understanding the cognitive profiles of individual cases and the clinical aspects of the illness/syndrome is stressed. Finally, the utility of the model for explaining how we process other situations that require an appreciation of others' intentions, thoughts, and beliefs is discussed.

Conceptual processing during the conscious resting state. A functional MRI study

Localized, task-induced decreases in cerebral blood flow are a frequent finding in functional brain imaging research but remain poorly understood. One account of these phenomena postulates processes ongoing during conscious, resting states that are interrupted or inhibited by task performance. Psychological evidence suggests that conscious humans are engaged almost continuously in adaptive processes involving semantic knowledge retrieval, representation in awareness, and directed manipulation of represented knowledge for organization, problem-solving, and planning. If interruption of such 'conceptual' processes accounts for task-induced deactivation, tasks that also engage these conceptual processes should not cause deactivation. Furthermore, comparisons between conceptual and nonconceptual tasks should show activation during conceptual tasks of the same brain areas that are 'deactivated' relative to rest. To test this model, functional magnetic resonance imaging data were acquired during a resting state, a perceptual task, and a semantic retrieval task. A network of left-hemisphere polymodal cortical regions showed higher signal values during the resting state than during the perceptual task but equal values during the resting and semantic conditions. This result is consistent with the proposal that perceptual tasks interrupt processes ongoing during rest that involve many of the same brain areas engaged during semantic retrieval. As further evidence for this model, the same network of brain areas was activated in two direct comparisons between semantic and perceptual processing tasks. This same 'conceptual processing' network was also identified in several previous studies that contrasted semantic and perceptual tasks or resting and active states. The model proposed here offers a unified account of these findings and may help to explain several unanticipated results from prior studies of semantic processing.

Rapid assessment of regional cerebral metabolic abnormalities in single subjects with quantitative and nonquantitative [18F]FDG PET: A clinical validation of statistical parametric mapping

The [18F]fluorodeoxyglucose ([18F]FDG) method for measuring brain metabolism has not the wide clinical application that one might expect, partly because of its high cost and the complexity of the quantification procedure, but also because of reporting techniques based on region of interest (ROI) analysis, which are time-consuming and not fully objective. In this paper we report a clinical validation of statistical parametric mapping (SPM) using rCMRglc (quantitative) and radioactivity distribution (nonquantitative) [18F]FDG PET data. We show that a 10-min noninteractive voxel-based SPM analysis on a standard workstation enables objective assessment, including localization in stereotactic space, of regional glucose consumption abnormalities, whose reliability can be assessed on statistical and clinical grounds. Clinical validity was established using a small series of patients with degenerative or developmental disorders, including probable Alzheimer's disease, progressive aphasia, multiple sclerosis, developmental specific language impairment, and epilepsy. Analysis of quantitative and nonquantitative data showed the same pattern of results, suggesting that, for clinical purposes, quantitation and invasive arterial cannulation can be avoided. This should facilitate a wider application of the technique and the extension of SPM clinical analysis to H215O PET or high resolution SPECT perfusion studies.

Prefrontal involvement in "temporal bridging" and timing movement

Brain activity exclusively related to a temporal delay has rarely been investigated using modern brain imaging. In this study we exploited the temporal resolution of functional magnetic resonance imaging (fMRI) to characterise, by sinusoidal regression analysis, differential neuroactivation patterns induced in healthy subjects by two sensorimotor synchronization tasks different in their premovement delay of either 0.6 s or 5 s. The short event rate condition required rhythmic tapping, while the long event rate condition required timing of intermittent movements. Left rostral prefrontal cortex, medial frontal cortex, SMA and supramarginal gyrus demonstrated increased MR signal intensity during low frequency synchronization, suggesting that these brain regions form a distributed neural network for cognitive time management processes, such as time estimation and motor output timing. Medial frontal cortex showed a biphasic pattern of response during both synchronization conditions, presumably reflecting frequency-independent motor output related attention. As predicted, sensorimotor and visual association areas demonstrated increased MR signal intensity during high frequency synchronization.

Hemispheric differences in context sensitivity during lexical ambiguity resolution

Three experiments were conducted to investigate the influence of contextual constraint on lexical ambiguity resolution in the cerebral hemispheres. A cross-modal priming variant of the divided visual field task was utilized in which subjects heard sentences containing homonyms and made lexical decisions to targets semantically related to dominant and subordinate meanings. Experiment 1 showed priming in both hemispheres of dominant meanings for homonyms embedded in neutral sentence contexts. Experiment 2 showed priming in both hemispheres of dominant and subordinate meanings for homonyms embedded in sentence contexts that biased a central semantic feature of the subordinate meaning. Experiment 3 showed priming of dominant meanings in the left hemisphere (LH), and priming of the subordinate meaning in the right hemisphere (RH) for homonyms embedded in sentences that biased a peripheral semantic feature of the subordinate meaning. These results are consistent with a context-sensitive model of language processing that incorporates differential sensitivity to semantic relationships in the cerebral hemispheres.

Focal cortical release of endogenous opioids during reading-induced seizures

BACKGROUND

Studies in animals implicate endogenous release of opioid peptides as a mechanism for terminating partial and generalised seizures. To localise dynamic changes in opioid neurotransmission associated with partial seizures and higher cognitive function, we investigated the release of endogenous opioids in patients with reading-induced seizures compared with healthy controls.

METHODS

Five patients who had reading epilepsy and six controls had 11C-diprenorphine (DPN) positron-emission-tomography (PET) scans while reading a string of symbols (baseline) or a scientific paper (activation). Statistical parametric mapping was used to find areas with differences in opioid-receptor binding.

FINDINGS

On activation scans mean 11C-DPN binding to opioid receptors was significantly lower (p<0.05 corrected for multiple non-independent comparisons) in the left parieto-temporo-occipital cortex (Brodmann area 37) in reading-epilepsy patients compared with controls.

INTERPRETATION

These findings suggest that opioid-like substances are involved in the termination of reading-induced seizures.

Functional anatomy of dominance for speech comprehension in left handers vs right handers

In order to study the functional anatomy of hemispheric dominance for language comprehension we compared the patterns of activations and deactivations with PET and H(2)15O during a story-listening task in two groups of normal volunteers selected on the basis of their handedness. The reference task was a silent rest. The results showed asymmetrical temporal activations favoring the left hemisphere in right handers (RH) together with Broca's area and medial frontal activations. A rightward lateralization of deactivations located in the parietal and inferior temporal gyrus was also observed. In left handers (LH) the temporal activations were more symmetrical as were the parietal and inferior frontal deactivations. Broca's area and medial frontal gyrus activations were present in LH. The direct comparison of RH and LH activations revealed larger activations in the left superior temporal, in particular in the left planum temporale and temporal pole of RH, while LH activated an additional right middle temporal region. Individual analysis of LH differences images superimposed on individual MRI planes demonstrated an important variability of functional dominance, with two LH leftward lateralized, two symmetrical, and one showing a rightward lateralization of temporal activations. There was no relationship between functional dominance and handedness scores. These results are in accordance with data from aphasiology that suggest a greater participation of the right hemisphere in language processing in LH. In addition, the presence of bilateral deactivations of the dorsal route could support the assumption that LH ambilaterality concerns, in addition to language, other cognitive functions such as visuospatial processing.

Cerebral hemispheric asymmetries in processing lexical metaphors

This study investigated semantic priming for literal (stinging-mosquito) and metaphoric (stinging-insult) associates presented to either the left or right visual fields (RVF/LVF) across stimulus-onset-asynchronies (SOA) of 200 and 800 ms. For the short SOA condition, facilitation was found for metaphorically related targets in both visual fields (VFs) while literally related targets were facilitated only in the RVF. For the long SOA condition, metaphorically related targets were facilitated in the LVF whereas literally related targets were facilitated in the RVF. These results support previous findings indicating an enhanced role of the RH in metaphoric comprehension. In addition, the present results are in accordance with current models of hemispheric semantic processing.

A functional neuroimaging description of two deep dyslexic patients

Deep dyslexia is a striking reading disorder that results from left-hemisphere brain damage and is characterized by semantic errors in reading single words aloud (e.g., reading 'spirit' as 'whisky'). Two types of explanation for this syndrome have been advanced. One is that deep dyslexia results from a residual left-hemisphere reading system that has lost the ability to pronounce a printed word without reference to meaning. The second is that deep dyslexia reflects right-hemisphere word processing. Although previous attempts to adjudicate between these hypotheses have been inconclusive, the controversy can now be addressed by mapping functional anatomy. In this study, we demonstrate that reading by two deep dyslexic patients (CJ and JG) involves normal or enhanced activity in spared left-hemisphere regions associated with naming (Broca's area and the left posterior inferior temporal cortex) and with the meanings of words (the left posterior temporo-parietal cortex and the left anterior temporal cortex). In the right-hemisphere homologues of these regions, there was inconsistent activation within the normal group and between the deep dyslexic patients. One (CJ) showed enhanced activity (relative to the normals) in the right anterior inferior temporal cortex, the other (JG) in the right Broca's area, and both in the right frontal operculum. Although these differential right-hemisphere activations may have influenced the reading behavior of the patients, their activation patterns primarily reflect semantic and phonological systems in spared regions of the left hemisphere. These results preclude an explanation of deep dyslexia in terms of purely right-hemisphere word processing.

Brain organization of language after early unilateral lesion: a PET study

Neuropsychological studies suggest that good long-term language outcome is possible following extensive early left-hemisphere damage. We explored the brain organization for language in children with early unilateral lesion, using [15O]-water PET. In 12 patients with left lesion (LL) and 9 patients with right lesion (RL), cerebral blood flow changes during listening to sentences and repetition were studied. A rightward shift of language activations in the LL group was found in perisylvian areas and multiple other, mostly temporo-parietal, regions. The hypothesis of intrahemispheric reorganization in the LL group found only limited support. The number of activated regions was overall greater in the RL group. Unexpected findings included a stronger subcortical and cerebellar language involvement in the RL group. We suggest that (a) early left lesion is associated with enhanced language participation of the right hemisphere in and beyond the classical language areas, and (b) postlesional effects are in part additive (recruitment of noncanonical areas), in part subtractive (functional depression in areas normally involved in language).

Structural divisions and functional fields in the human cerebral cortex

The question of what is a cortical area needs a thorough definition of borders both in the microstructural and the functional domains. Microstructural parcellation of the human cerebral cortex should be made on multiple criteria based on quantitative measurements of microstructural variables, such as neuron densities, neurotransmitter receptor densities, enzyme densities, etc. Because of the inter-individual variations of extent and topography of microstructurally defined areas, the final microstructurally defined areas appear as population maps. In the functional domain, columns, patches and blobs signifying synaptically active parts of the cortex appear as cortical functional fields. These fields are the largest functional entities of the cerebral cortex according to the cortical field hypothesis. In its strong version, the cortical field hypothesis postulates that all neurons and synapses within the fields perform a co-operative computation. A number of such fields together provide the functional contribution of the cerebral cortex. The functional parcellation of the human cerebral cortex must be based on field population maps, which after intersection analysis appear as functional domains. The major structural-functional hypothesis to be examined is whether these functional domains are equi-territorial to the microstructurally defined meta-maps. The cortical hypothesis predicts that, if two brain tasks make use of one or several identical or largely overlapping fields, they cannot be performed simultaneously without errors or increases in latency. Evidence for such interference is presented. This evidence represents a restriction in the parallel processing of the human brain. In the posterior part of the brain not only visual cortical areas may qualify for parallel processing, but also the somatosensory cortices appear to have separate functional streams for the detection of microgeometry and macrogeometry.

Cerebral hemispheric asymmetries in processing lexical metaphors

This study investigated semantic priming for literal (stinging-mosquito) and metaphoric (stinging-insult) associates presented to either the left or right visual fields (RVF/LVF) across stimulus-onset-asynchronies (SOA) of 200 and 800 ms. For the short SOA condition, facilitation was found for metaphorically related targets in both visual fields (VFs) while literally related targets were facilitated only in the RVF. For the long SOA condition, metaphorically related targets were facilitated in the LVF whereas literally related targets were facilitated in the RVF. These results support previous findings indicating an enhanced role of the RH in metaphoric comprehension. In addition, the present results are in accordance with current models of hemispheric semantic processing.

Distinct brain loci in deductive versus probabilistic reasoning

Deductive versus probabilistic inferences are distinguished by normative theories, but it is unknown whether these two forms of reasoning engage similar cerebral loci. To clarify the matter, positron emission tomography was applied during deductive versus probabilistic reasoning tasks, using identical stimuli. Compared to a language comprehension task involving the same stimuli, both probabilistic and deductive reasoning increased regional cerebral blood flow (rCBF) bilaterally in the mesial frontal region and in the cerebellum. In the direct comparison, probabilistic reasoning increased rCBF in left dorsolateral frontal regions, whereas deductive reasoning enhanced rCBF in associative occipital and parietal regions, with a right hemispheric prevalence. The results suggest that reasoning about syllogisms engages distinct brain mechanisms, depending on the intention to evaluate them deductively versus probabilistically.

Neural correlates of the episodic encoding of pictures and words

A striking characteristic of human memory is that pictures are remembered better than words. We examined the neural correlates of memory for pictures and words in the context of episodic memory encoding to determine material-specific differences in brain activity patterns. To do this, we used positron emission tomography to map the brain regions active during encoding of words and pictures of objects. Encoding was carried out by using three different strategies to explore possible interactions between material specificity and types of processing. Encoding of pictures resulted in greater activity of bilateral visual and medial temporal cortices, compared with encoding words, whereas encoding of words was associated with increased activity in prefrontal and temporoparietal regions related to language function. Each encoding strategy was characterized by a distinctive activity pattern, but these patterns were largely the same for pictures and words. Thus, superior overall memory for pictures may be mediated by more effective and automatic engagement of areas important for visual memory, including medial temporal cortex, whereas the mechanisms underlying specific encoding strategies appear to operate similarly on pictures and words.

Anatomical variability in the cortical representation of first and second language

Functional magnetic resonance imaging was used to assess inter-subject variability in the cortical representation of language comprehension processes. Moderately fluent French-English bilinguals were scanned while they listened to stories in their first language (L1 = French) or in a second language (L2 = English) acquired at school after the age of seven. In all subjects, listening to L1 always activated a similar set of areas in the left temporal lobe, clustered along the left superior temporal sulcus. Listening to L2, however, activated a highly variable network of left and right temporal and frontal areas, sometimes restricted only to right-hemispheric regions. These results support the hypothesis that first language acquisition relies on a dedicated left-hemispheric cerebral network, while late second language acquisition is not necessarily associated with a reproducible biological substrate. The postulated contribution of the right hemisphere to L2 comprehension is found to hold only on average, individual subjects varying from complete right lateralization to standard left lateralization for L2.

Regional cerebral blood flow changes related to affective speech presentation in persistent vegetative state

A story told by his mother was presented on tape to a trauma patient in persistent vegetative state (PVS). During auditory presentation, measurements of regional cerebral blood flow (rCBF) were performed by means of positron emission tomography (PET). Changes in rCBF related to this stimulus condition, as compared to presenting non-word sound, were evaluated by means of statistical parametric mapping (SPM). This analysis indicated activation of rostral anterior cingulate, right middle temporal and right premotor cortices, which may reflect appropriate cortical involvement in processing emotional attributes of sound or speech.

Factors that influence effect size in 15O PET studies: a meta-analytic review

The PET literature is growing exponentially, creating a need and an opportunity to perform a meta-analytic review consolidating the published information. This study describes the use of effect size as an index in PET studies and discusses how this measure can be used for comparing findings across studies, laboratories, and paradigms. In comparing studies across laboratories it is essential to know how the methods employed affect the results and conclusions drawn. This study also compared effect size for two different methods of tracer delivery in 15O PET studies ([15O]H2O bolus injection versus inhalation of [15O]CO2), whether averaged versus single-scan conditions were used, and the data analytic strategy employed. The effect sizes observed across studies were consistently large with a median effect size of 8.55, indicating that the phenomena investigated in 15O PET studies are strong. The largest peak activation reported in a study was found to be affected by variability in sample size, data analytic strategy, and repeat versus single-scan conditions. However, the impact of these factors was not examined on smaller or less intense peaks. Minimal standards for reporting statistical results are discussed.

Functional Neuroanatomy of Recall and Recognition: A PET Study of Episodic Memory

The purpose of this study was to directly compare the brain regions involved in episodic-memory recall and recognition. Changes in regional cerebral blood flow were measured by positron emission tomography while young healthy test persons were either recognizing or recalling previously studied word pairs. Reading of previously nonstudied pairs served as a reference task for subtractive comparisons. Compared to reading, both recall and recognition were associated with higher blood flow (activation) at identical sites in the right prefrontal cortex (areas 47, 45, and 10) and the anterior cingulate. Compared to recognition, recall was associated with higher activation in the anterior cingulate, globus pallidus, thalamus, and cerebellum, suggesting that these components of the cerebello-frontal pathway play a role in recall processes that they do not in recognition. Compared to recall, recognition was associated with higher activation in the right inferior parietal cortex (areas 39, 40, and 19), suggesting a larger perceptual component in recognition than in recall. Contrary to the expectations based on lesion data, the activations of the frontal regions were indistinguishable in recall and recognition. This finding is consistent with the notion that frontal activations in explicit memory tasks are related to the general episodic retrieval mode or retrieval attempt, rather than to specific mechanisms of ecphory (recovery of stored information).

Human brain language areas identified by functional magnetic resonance imaging

Functional magnetic resonance imaging (FMRI) was used to identify candidate language processing areas in the intact human brain. Language was defined broadly to include both phonological and lexical-semantic functions and to exclude sensory, motor, and general executive functions. The language activation task required phonetic and semantic analysis of aurally presented words and was compared with a control task involving perceptual analysis of nonlinguistic sounds. Functional maps of the entire brain were obtained from 30 right-handed subjects. These maps were averaged in standard stereotaxic space to produce a robust "average activation map" that proved reliable in a split-half analysis. As predicted from classical models of language organization based on lesion data, cortical activation associated with language processing was strongly lateralized to the left cerebral hemisphere and involved a network of regions in the frontal, temporal, and parietal lobes. Less consistent with classical models were (1) the existence of left hemisphere temporoparietal language areas outside the traditional "Wernicke area," namely, in the middle temporal, inferior temporal, fusiform, and angular gyri; (2) extensive left prefrontal language areas outside the classical "Broca area"; and (3) clear participation of these left frontal areas in a task emphasizing "receptive" language functions. Although partly in conflict with the classical model of language localization, these findings are generally compatible with reported lesion data and provide additional support for ongoing efforts to refine and extend the classical model.

Lateralization of affective prosody in brain and the callosal integration of hemispheric language functions

Although affective prosody appears to be a dominant function of the right hemisphere, its degre of lateralization has not yet been established since various publications have reported affective-prosodic deficits following left brain damage in association with aphasia. This paper explores the mechanisms underlying affective-prosodic deficits following left and right brain damage by testing the ability of subjects to repeat and comprehend affective prosody under progressively reduced verbal-articulatory conditions. The results demonstrate that reducing verbal-articulatory conditions robustly improves the performance of left but not right brain damaged patients, a finding that supports the supposition that affective prosody is strongly lateralized to the right hemisphere. However, the performance of left brain damaged patients was not correlated to the presence, severity, or type of aphasic deficit(s). Based on functional-anatomic correlations for spontaneous affective prosody and affective-prosodic repetition, deep white matter lesions located below the supplementary motor area that disrupt interhemispheric connections coursing through the mid-rostral corpus callosum may contribute to affective-prosodic deficits that are both additive and independent of any aphasic deficits. In light of these and other findings, various anatomical, functional, and maturational hierarchic relationships between the affective-prosodic and verbal-linguistic aspects of language are posited in order to help further explain discrepancies that exist in the literature regarding the neurology of affective prosody.

The neural regions sustaining object recognition and naming

This positron emission tomography study dissociates the neural correlates of object recognition and naming. Stimuli comprised coloured outline drawings of objects and coloured nonsense shapes. Subjects either viewed or explicitly named objects, similarly they viewed or named the colour of the shapes. Activations common to object and colour naming were identified by contrasting the explicit naming conditions (objects and colours) with the control (viewing) conditions. Activations associated with object recognition were identified by contrasting both object conditions (naming and viewing) with both shape conditions and activations specific to object or colour naming were identified by contrasting object naming (relative to object viewing) with colour naming (relative to shape viewing). The results associate: (i) object recognition with left middle occipital and bilateral anterior temporal cortices; (ii) modality independent naming with left posterior basal temporal lobe and the left prefrontal cortex; (iii) areas specific to object naming with left temporal extrasylvian regions, left anterior insula and right cerebellum; and (iv) areas specific to colour naming with left posterior lingual and fusiform gyri and midline cerebellum. These results are discussed in relation to previous neuroimaging and neuropsychological findings.

Assumptions and validations of statistical tests for functional neuroimaging

We contrast two statistical methods: three-dimensional cluster analysis and statistical parametric mapping. We show that three-dimensional cluster analysis is based on a neurobiological theory of the regulation of blood flow and, unlike statistical parametric mapping, carries a minimum of assumptions that are tested. Statistical parametric mapping is a formal approach, which is based on a multitude of assumptions of which the majority have not been validated. We also demonstrate that in practice three-dimensional cluster analysis has a reasonable balance between sensitivity and the probability of false positives, giving high reproducibility with data on e.g. colour discrimination.

Brain activation modulated by sentence comprehension

The comprehension of visually presented sentences produces brain activation that increases with the linguistic complexity of the sentence. The volume of neural tissue activated (number of voxels) during sentence comprehension was measured with echo-planar functional magnetic resonance imaging. The modulation of the volume of activation by sentence complexity was observed in a network of four areas: the classical left-hemisphere language areas (the left laterosuperior temporal cortex, or Wernicke's area, and the left inferior frontal gyrus, or Broca's area) and their homologous right-hemisphere areas, although the right areas had much smaller volumes of activation than did the left areas. These findings generally indicate that the amount of neural activity that a given cognitive process engenders is dependent on the computational demand that the task imposes.

Other minds in the brain: a functional imaging study of "theory of mind" in story comprehension

The ability of normal children and adults to attribute independent mental states to self and others in order to explain and predict behaviour ("theory of mind") has been a focus of much recent research. Autism is a biologically based disorder which appears to be characterised by a specific impairment in this "mentalising" process. The present paper reports a functional neuroimaging study with positron emission tomography in which we studied brain activity in normal volunteers while they performed story comprehension tasks necessitating the attribution of mental states. The resultant brain activity was compared with that measured in two control tasks: "physical" stories which did not require this mental attribution, and passages of unlinked sentences. Both story conditions, when compared to the unlinked sentences, showed significantly increased regional cerebral blood flow in the following regions: the temporal poles bilaterally, the left superior temporal gyrus and the posterior cingulate cortex. Comparison of the "theory of mind" stories with "physical" stores revealed a specific pattern of activation associated with mental state attribution: it was only this task which produced activation in the medial frontal gyrus on the left (Brodmann's area 8). This comparison also showed significant activation in the posterior cingulate cortex. These surprisingly clear-cut findings are discussed in relation to previous studies of brain activation during story comprehension. 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.

Analogical representation and language structure

Severe impairment of the analogue of mental representation is not compensated for by putative language-based cognitive processes in non-dysphasic brain-damaged patients. This undermines the hypothesis of an independent role for language in the generation of thought. Against this view it may be contended that there seems to be no obvious way in which analogical mental representation can decide between alternative syntactical structures available for the expression of thought. We performed a visual imagery experiment in which we asked 40 subjects to imagine visual scenes representing the meanings of simple utterances presented to them. The subjects then had to indicate the relative position, in each visual image, of two objects mentioned in each utterance. Series of utterances were presented differing syntactically (active or passive phrase) and semantically (specifying in different ways the spatial and temporal relations between the objects mentioned). The results of this mental imagery experiment indirectly support the hypothesis that syntactical structures can be represented in a nonlinguistic analogue medium.