Temporo-occipital Junction Research Articles

Ha Ha! Versus Aha! A Direct Comparison of Humor to Nonhumorous Insight for Determining the Neural Correlates of Mirth

While humor typically involves a surprising discovery, not all discoveries are perceived as humorous or lead to a feeling of mirth. Is there a difference in the neural signature of humorous versus nonhumorous discovery? Subjects viewed drawings that were uninterpretable until a caption was presented that provided either: 1) a nonhumorous interpretation (or insight) of an object from an unusual or partial view (UV) or 2) a humorous interpretation (HU) of the image achieved by linking remote and unexpected concepts. fMRI activation elicited by the UV captions was a subset of that elicited by the humorous HU captions, with only the latter showing activity in the temporal poles and temporo-occipital junction (linking remote concepts), and medial prefrontal cortex (unexpected reward). Mirth may be a consequence of the linking of remote ideas producing high-and unexpected-activation in association and classical reward areas. We suggest that this process is mediated by opioid activity as part of a system rewarding attention to novel information.

Extensive anterior skull-base mesenchymal chondrosarcoma: unusual cause of multiple indolent masses on the forehead

Primary intracranial occurrence of an extraskeletal mesenchymal chondrosarcoma (MC) is unusual. The commonly involved sites are the orbit, clivus and temporo-occipital junction. Occurrence of the lesion in the anterior skull-base (ASB) in an infiltrative manner and with extra-calvarial involvement, is anecdotal. We report the case of a 35-year-old woman who presented with two indolent swellings on the forehead for a duration of 1 year. Examination revealed impaired visual acuity and complete external ophthalmoplegia in the right eye and 5 × 6 cm and 2 × 3 cm sized hard masses on the forehead. CT and MRI revealed a large, intensely enhancing ASB mass with extensions into the right orbit, ethmoid sinus, nasal cavity, and anteriorly, into the subcutaneous tissue of the frontal scalp through erosions in the bone. At surgery via a right frontal recraniotomy, the lesion was found to be firm and very vascular. Owing to its extreme vascularity, decompression was limited to excision of the intracranial and extra-calvarial components of the lesion. Histopathology was consistent with the diagnosis of MC. The patient was advised a second stage surgery for excision of the residual lesion. She, however, opted for radiation therapy and was lost to follow-up. This report, with one of the most extensive ASB MCs described to date, adds to the list of rare differentials of indolent forehead masses in the diagnostic armamentarium of the neuropathologist.

In Reply

In Reply: We thank Dr Bartsch and colleagues for their commentary. The authors raise several interesting points, such as the reduction of false-negative trackings using probabilistic tractography with crossing fibers modeling, and the high risk of reading impairment if the left inferior parietal lobe is damaged. We appreciate their favorable assessment of our article and agree with their correction. Specifically, the most lateral component of the temporoparietal fiber intersection area (TPFIA) is not the horizontal portion, but the vertical portion of the superior longitudinal fasciculus (SLF).1 However, the vertical portion of the SLF should be differentiated from the vertical occipital fasciculus (VOF) (Figure). Classical anatomical studies describe the VOF or Wernicke perpendicular fasciculus as a connection between the superior occipital gyrus and the posterior parietal lobe superiorly, and the fusiform gyrus at the temporal base inferiorly.2 Recent diffusion tensor imaging studies describe the VOF as a tract located within the occipital lobe, specifically connecting the occipitotemporal sulcus to the lateral portion of the occipital parietal junction.3 The tract described in our article is not connected to the occipital lobe, because it is located at the temporoparietal junction. As we had previously described, this tract connects the posterior portion of the inferior parietal lobe (ie, angular gyrus) with the middle temporal gyrus,4 and corresponds to the connection described by Catani and colleagues as the vertical portion of the SLF.5FIGURE: A, fiber dissection of the tracts that pass through the temporoparietal fiber intersection area (TPFIA) in a left hemisphere. The vertical portion of the superior longitudinal fasciculus (SLF) has been tilted superiorly to expose the arcuate fasciculus. The vertical portion of the SLF is located at the temporoparietal junction and connects the posterior portion of the inferior parietal lobe (ie, angular gyrus) with the middle temporal gyrus. B, the vertical portion of the SLF was removed. The vertical occipital fasciculus (VOF) was dissected, and small pieces of paper were placed underneath this tract to demonstrate that it was completely separated from the deeper structures. It is evidenced that the VOF is located posterior to the TPFIA, specifically within the occipital lobe. The VOF connects the superior occipital gyrus with the temporo-occipital junction. C, schematic representation of the same tracts presented in A and B. 1 = vertical portion of the SLF; 2 = arcuate fasciculus; 3 = VOF. CS, central sulcus; PCG, precentral gyrus; MTG, middle temporal gyrus; SMG, supramarginal gyrus; STG, superior temporal gyrus.It is important to emphasize that the SLF is the most complex connection in the human brain, and that the available descriptions of this tract provide basic anatomic information. Further anatomical and functional studies are needed because the detailed understanding of this bundle remains to be ascertained. Disclosures Dr Martino receives specific funding from the 11/18 API grant entitled “Estudio de la conectividad conectividad cerebral mediante disección de fibras estructural.” “Fundación Marqués de Valdecilla,” IFIMAV, Santander, Cantabria, Spain. October, 8, 2010. The authors have no personal financial or institutional interest in any of the drugs, materials, or devices described in this article.

Dreaming and the Default Mode Network

This article makes a brief contribution to the ongoing dialogue on dreams between neuroscience and psychoanalysis by linking several converging lines of evidence. Recent evidence indicates that the default mode network (DMN), a highly interconnected set of “hubs” in the brain, is active during sleep. In addition, activity in the DMN is strongly associated with mental imagery that is not directly tied to current perception (“stimulus-independent thought”), which is also a central feature of dreams. Finally, the elimination of dreams is correlated with lesions in areas that have a high degree of overlap with two regions of the DMN, the ventromedial prefrontal cortex (vmPFC) and the temporo-occipital junction. Given that the vmPFC is a key node in brain circuitry regulating motivation, these converging lines of evidence support the basic psychoanalytic idea that dreams arise from wishful impulses and other emotional motivations.

Hemispheric Asymmetry for Affective Stimulus Processing in Healthy Subjects–A fMRI Study

BackgroundWhile hemispheric specialization of language processing is well established, lateralization of emotion processing is still under debate. Several conflicting hypotheses have been proposed, including right hemisphere hypothesis, valence asymmetry hypothesis and region-specific lateralization hypothesis. However, experimental evidence for these hypotheses remains inconclusive, partly because direct comparisons between hemispheres are scarce.MethodsThe present fMRI study systematically investigated functional lateralization during affective stimulus processing in 36 healthy participants. We normalized our functional data on a symmetrical template to avoid confounding effects of anatomical asymmetries. Direct comparison of BOLD responses between hemispheres was accomplished taking two approaches: a hypothesis-driven region of interest analysis focusing on brain areas most frequently reported in earlier neuroimaging studies of emotion; and an exploratory whole volume analysis contrasting non-flipped with flipped functional data using paired t-test.ResultsThe region of interest analysis revealed lateralization towards the left in the medial prefrontal cortex (BA 10) during positive stimulus processing; while negative stimulus processing was lateralized towards the right in the dorsolateral prefrontal cortex (BA 9 & 46) and towards the left in the amygdala and uncus. The whole brain analysis yielded similar results and, in addition, revealed lateralization towards the right in the premotor cortex (BA 6) and the temporo-occipital junction (BA 19 & 37) during positive stimulus processing; while negative stimulus processing showed lateralization towards the right in the temporo-parietal junction (BA 37,39,42) and towards the left in the middle temporal gyrus (BA 21).ConclusionOur data suggests region-specific functional lateralization of emotion processing. Findings show valence asymmetry for prefrontal cortical areas and left-lateralized negative stimulus processing in subcortical areas, in particular, amygdala and uncus.

The morphology and variability of the caudal rami of the superior temporal sulcus

The caudal branches of the superior temporal sulcus (cSTS) have been difficult to characterize because of the considerable degree of morphological variability across individuals. Leading atlases of the human brain are inconsistent with each other in terms of the number of branches identified and the nomenclature used to refer to them. Examination of the magnetic resonance images (MRIs) of 45 human brains (90 hemispheres) demonstrates three branches of the cSTS that ascend into the inferior parietal lobule: an anterior branch (cSTS1), a central branch (cSTS2) and a posterior branch (cSTS3). The cSTS1 is found immediately posterior to the ascending limb of the Sylvian fissure, followed by the cSTS2, and then the last branch, cSTS3, at the parieto-occipital junction. The temporal part of the STS joins most frequently with the cSTS2 (approximately 60% of cases), the cSTS1 (approximately 30% of cases) and least frequently with the cSTS3 (approximately 10% of cases). At the temporo-occipital junction, there is another sulcus that is related to the STS, the ventral anterior occipital sulcus (AOCS-v), a sulcus that has been functionally linked to area MT/v5 in the human brain. While the STS may appear to join AOCS-v from the surface of the brain, it can be established from examination of the depth of the sulci that they are not continuous. The variability in location of each one of the cSTS branches is expressed quantitatively in the MNI standard proportional stereotaxic space.

Film Excerpts Shown to Specifically Elicit Various Affects Lead to Overlapping Activation Foci in a Large Set of Symmetrical Brain Regions in Males

While the limbic system theory continues to be part of common scientific parlance, its validity has been questioned on multiple grounds. Nonetheless, the issue of whether or not there exists a set of brain areas preferentially dedicated to emotional processing remains central within affective neuroscience. Recently, a widespread neural reference space for emotion which includes limbic as well as other regions was characterized in a large meta-analysis. As methodologically heterogeneous studies go into such meta-analyses, showing in an individual study in which all parameters are kept constant, the involvement of overlapping areas for various emotion conditions in keeping with the neural reference space for emotion, would serve as valuable confirmatory evidence. Here, using fMRI, 20 young adult men were scanned while viewing validated neutral and effective emotion-eliciting short film excerpts shown to quickly and specifically elicit disgust, amusement, or sexual arousal. Each emotion-specific run included, in random order, multiple neutral and emotion condition blocks. A stringent conjunction analysis revealed a large overlap across emotion conditions that fit remarkably well with the neural reference space for emotion. This overlap included symmetrical bilateral activation of the medial prefrontal cortex, the anterior cingulate, the temporo-occipital junction, the basal ganglia, the brainstem, the amygdala, the hippocampus, the thalamus, the subthalamic nucleus, the posterior hypothalamus, the cerebellum, as well as the frontal operculum extending towards the anterior insula. This study clearly confirms for the visual modality, that processing emotional stimuli leads to widespread increases in activation that cluster within relatively confined areas, regardless of valence.

Investigating relationships between cortical thickness and cognitive performance in patients with schizophrenia and healthy adults

Relationships between prefrontal and temporal lobe grey matter volumes as assessed by magnetic resonance imaging and neurocognitive test results have been reported in schizophrenia. This investigation aimed to localize brain regions where cortical thickness and neurocognitive performance were related, and investigate if such relationships might differ in schizophrenia patients and healthy controls. Sixty-seven patients with schizophrenia and 69 healthy controls were characterized by neurocognitive testing and by brain cortical thickness maps. Putative cortical thickness/cognitive score relationships were investigated with contrast analyses of general linear models for the combined sample. Regions in which relationships were present were further investigated for diagnostic interaction. In the combined sample, significant positive relationships were found between frontal, temporal and occipital regions and tests for verbal IQ, verbal learning and executive functions. Diagnostic interaction was found for the relationships between verbal IQ and the right temporo-occipital junction and the left middle occipital gyrus. In conclusion, the significant relationships between cortical thickness and neurocognitive performances were localized in brain areas known to be involved in cognition. The relationships were similar in patients and controls, except for the right temporo-occipital and left occipital cortical areas, indicating a disrupted structure–function relationship in patients with schizophrenia compared to healthy control subjects.

Cognitive and neural basis of the consistency and lexicality effects in reading Chinese

This study aims to investigate the underlying cognitive mechanisms of Chinese orthography-to-phonology transformation and its neural correlates. A behavioral study demonstrated that the phonetic radical can be used to suggest the pronunciation of a Chinese pseudocharacter based on the type frequency of the pronunciations associated with its constituent phonetic radical, rather than just to sound out its constituent phonetic radical. The follow-up event-related fMRI (functional magnetic resonance imaging) study further manipulated the lexicality and the phonetic consistency and showed higher brain activations in the left inferior and middle frontal gyrus, the left temporoparietal region (inferior parietal gyrus and supramarginal gyrus), and the left temporooccipital junction for reading low consistency characters compared to high consistency ones. A similar activation pattern can be observed when distinguishing between the brain activation involved when reading pseudocharacters and characters. However, the angular gyrus appears to be activated under the consistency effect in reading pseudocharacters but not for reading words. The contributions of these regions to Chinese orthography-to-phonology transformation are discussed and compared with those of the alphabetic writing system.

Evidence for an occipito-temporal tract underlying visual recognition in picture naming

A 24-year-old male underwent awake surgery for a lesion in the left dominant basal temporo-occipital junction. During the intraoperative functional mapping using picture naming, cortical stimulation near the visual word form area led to visual paraphasia. These visual paraphasias were also elicited axonally by subcortical stimulation at the anterior wall of the cavity. We propose to discuss the existence of this “visual object form area”, devoted to the visual recognition of object, and its links with the closely related “visual word form area”. We suggest that its afference, whose stimulation also induced visual paraphasias, may be one part of the U-shaped fibers distributed along the posterior part of the occipito-temporal connection system (inferior longitudinal fasciculus). Preservation of this white matter tract is essential for visual recognition. Thus, it should be mapped intraoperatively more systematically.

Neural integration of iconic and unrelated coverbal gestures: a functional MRI study.

Gestures are an important part of interpersonal communication, for example by illustrating physical properties of speech contents (e.g., "the ball is round"). The meaning of these so-called iconic gestures is strongly intertwined with speech. We investigated the neural correlates of the semantic integration for verbal and gestural information. Participants watched short videos of five speech and gesture conditions performed by an actor, including variation of language (familiar German vs. unfamiliar Russian), variation of gesture (iconic vs. unrelated), as well as isolated familiar language, while brain activation was measured using functional magnetic resonance imaging. For familiar speech with either of both gesture types contrasted to Russian speech-gesture pairs, activation increases were observed at the left temporo-occipital junction. Apart from this shared location, speech with iconic gestures exclusively engaged left occipital areas, whereas speech with unrelated gestures activated bilateral parietal and posterior temporal regions. Our results demonstrate that the processing of speech with speech-related versus speech-unrelated gestures occurs in two distinct but partly overlapping networks. The distinct processing streams (visual versus linguistic/spatial) are interpreted in terms of "auxiliary systems" allowing the integration of speech and gesture in the left temporo-occipital region.

FMRI correlates of visuo‐spatial reorienting investigated with an attention shifting double‐cue paradigm

The control of visuo-spatial attention entails the joint contribution of goal-directed (endogenous) and stimulus-driven (exogenous) factors. However, little is known about the neural bases of the interplay between these two mechanisms. To address this issue, we presented endogenous (spatially informative) and exogenous (noninformative) visual cues sequentially within the same trial (double-cue paradigm) during fMRI, crossing factorially the validity of the two cues. We found that both endogenous and exogenous cues affected behavioral performance, speeding-up or slowing-down target discrimination when valid and invalid, respectively. Despite the double-cue paradigm maximizes the interplay between endogenous and exogenous factors, the two types of cue affected responses in an independent manner without any significant effect of congruence. The imaging data revealed increased activation in separate cortical areas following invalid endogenous and invalid exogenous cues. A fronto-parietal system was activated during invalid endogenous trials, whereas a region at the temporo-occipital junction was activated during invalid exogenous trials. Within both circuits, activity was unaffected by the validity of the other cue. These results indicate the existence of separate, noninteracting neural circuits for endogenous and exogenous reorienting of visuo-spatial attention.

Augmented neural activity during executive control processing following diffuse axonal injury

Deficits in working memory are commonly observed after traumatic brain injury (TBI), with executive control processes preferentially impacted relative to storage and rehearsal. Previous activation functional neuroimaging investigations of working memory in patients with TBI have reported altered functional recruitment, but methodologic issues including sample heterogeneity (e.g., variability in injury mechanism, severity, neuropathology or chronicity), underspecified definitions of "working memory," and behavioral differences between TBI and control groups have hindered interpretation of these changes. Executive control processing in working memory was explicitly engaged during fMRI in a sample of carefully selected chronic-stage, moderate-to-severe TBI patients with diffuse axonal injury (DAI) but without focal lesions. Despite equivalent task performance, we observed a pattern of greater recruitment of interhemispheric and intrahemispheric regions of prefrontal cortex (PFC) and posterior cortices in our DAI sample. Enhanced activations were recorded in the left dorsolateral PFC (middle frontal gyrus), right ventrolateral PFC (inferior frontal gyrus), bilateral posterior parietal cortices, and left temporo-occipital junction. Region-of-interest analyses confirmed that these effects were robust across individual patients and could not be attributed to load factors or slowed speed of processing. Augmented functional recruitment in the context of normal behavioral performance may be a neural marker of capacity or efficiency limits that can affect functional outcome after traumatic brain injury with diffuse injury.

Objects and their icons in the brain: The neural correlates of visual concept formation

We are constantly exposed to symbols such as traffic signs, emoticons in internet communication, or other abstract representations of objects as well as, of course, the written words. However, aside from the word reading, little is known about the way our brain responds when we read non-lexical iconic symbols. By using functional MRI, we found that the watching of icons recruited manifold brain areas including frontal and parietal cortices in addition to the temporo-occipital junction in the ventral pathway. Remarkably, the brain response for icons was contrasted with the response for corresponding concrete objects with the pattern of 'hyper-cortical and hypo-subcortical' brain activation. This neural underpinning might be called the neural correlates for visual concept formation.

High-frequency oscillations in distributed neural networks reveal the dynamics of human decision making

We examine the relative timing of numerous brain regions involved in human decisions that are based on external criteria, learned information, personal preferences, or unconstrained internal considerations. Using magnetoencephalography (MEG) and advanced signal analysis techniques, we were able to non-invasively reconstruct oscillations of distributed neural networks in the high-gamma frequency band (60–150 Hz). The time course of the observed neural activity suggested that two-alternative forced choice tasks are processed in four overlapping stages: processing of sensory input, option evaluation, intention formation, and action execution. Visual areas are activated first, and show recurring activations throughout the entire decision process. The temporo-occipital junction and the intraparietal sulcus are active during evaluation of external values of the options, 250–500 ms after stimulus presentation. Simultaneously, personal preference is mediated by cortical midline structures. Subsequently, the posterior parietal and superior occipital cortices appear to encode intention, with different subregions being responsible for different types of choice. The cerebellum and inferior parietal cortex are recruited for internal generation of decisions and actions, when all options have the same value. Action execution was accompanied by activation peaks in the contralateral motor cortex. These results suggest that high-gamma oscillations as recorded by MEG allow a reliable reconstruction of decision processes with excellent spatiotemporal resolution.

Activation differences in observation of hand movements for imitation or velocity judgement

We aimed to investigate the brain areas engaged in observation of hand movements with the intention of imitation or judging movement velocity. Both processes reflect different analytic approaches in movement observation. We were interested if these two processes can be distinguished or share common activation foci. Twelve healthy, right-handed volunteers were required to observe video clips of hand gestures and of object related grasping movements while the regional cerebral blood flow was measured using positron emission tomography. The subjects were instructed either to imitate the actions or to judge the velocity of the observed movements after scanning. Action observation with the instruction to judge movement velocity engaged bilaterally the temporo-occipital junction and adjacent visual cortical areas. In contrast, observation with the instruction to imitate them afterwards, yielded large activation clusters covering the left parietal and premotor cortex. Both contrasts demonstrated activation in the inferior frontal cortex, however, on opposite sides. Results suggest that movement observation with the goal of imitation activated specific areas of the parietal cortex in the dominant hemisphere probably related to programming of the movement kinematics. In contrast, observation with the goal to characterize the velocity of the finger movements activated the ventral visual pathways. Thus, movement observation recruits non-overlapping cortical networks, depending on the information attended to which are characterised by a dorsal ventral dissociation.

IC-P-078: Brain SPECT patterns associated with different profiles of memory impairment in amnestic MCI

In view of upcoming treatment options for AD in the predementia stage, it is crucial to identify features that predict conversion to AD within a population of amnestic MCI (aMCI). It has been suggested that MCI of AD type may present with a memory profile indicating medial temporal lobe dysfunction. We recently demonstrated that patients with aMCI and mild AD are impaired on a visual recognition memory task (DMS48). This finding may be related to early neuropathological change in rhinal cortices, thought to be crucial for visual recognition memory. The aim of this study was to characterize the pattern of brain SPECT perfusion of patients with mild aMCI according to their performance on the DMS48. 26 patients with mild aMCI were divided in two subgroups according to their Z–score on the DMS48. 13 patients obtained a Z–score ≤ –1.5 (“DMS48+ group”) and 13 below (“DMS48– group”). Mean age and MMSE score did not differ between the two groups (69yrs ±7; MMSE score: 27.4±1). Brain perfusion was studied using 99mTc–ECD SPECT. A voxel–by–voxel group analysis was performed with SPM2 (p<0.01c). In the DMS48+ group, hypoperfusion of the left prefrontal cortex was found, including orbitoventral and dorsolateral areas (Figure A). In contrast, in the DMS48– group, bilateral hypoperfusion of medial temporal lobe structures and temporobasal cortices extending to the temporo–occipital junction on both sides was observed. In this group, there was also bilateral hypoperfusion of the temporo–parietal associative cortex and right posterior cingulum (Figure B). Two groups of patients with mild aMCI, classified according to their performance on a visual recognition memory task, were found to exhibit distinctive patterns of cerebral hypoperfusion. The DMS48+ group showed left prefrontal hypoperfusion and no abnormality in medial temporal lobe structures. This suggests that their memory impairment may be related to prefrontal dysfunction that interferes with encoding/retrieval processes, in particular for verbal material. The DMS48– group showed hypoperfusion in medial temporal lobes, in posterior associative cortex and in the cingulum, a pattern usually described in early AD. Combined SPECT and evaluation of visual recognition memory may be useful to identify aMCI patients of the AD type.

Disturbed line bisection is associated with posterior brain lesions

Neglect patients classically fail to orient and respond to stimuli appearing on their contralesional side. Traditionally, the neglect syndrome has been associated with damage to the right inferior parietal lobule (IPL) and the right temporo-parietal junction (TPJ). Neglect is popularly assessed by two different tasks: line bisection and cancellation. In a previous study (S. Ferber, H.-O. Karnath, How to assess spatial neglect-line bisection or cancellation tasks. J. Clin. Exp. Neuropsychol. 23 (2001) 599–607), we observed that performance on the cancellation task correlates well with the characteristic behavioral disorders used to clinically diagnose spatial neglect, while line bisection was a poor predictor. This might indicate that the disability to correctly bisect lines is a distinct disorder separable from spatial neglect. Here, we assess the anatomy of the patients investigated in that study, and reveal that damage to the temporo-occipital junction correlates with poor performance in the line bisection task. This work extends previous work by Binder et al. (J. Binder, R. Marshall, R. Lazar, J. Benjamin, J.P. Mohr, Distinct syndromes of hemineglect. Arch. Neurol. 49 (1992) 1187–1194) suggesting that line bisection and cancellation identify distinct syndromes. The data suggest that these two tasks dissociate both in terms of behavior and anatomy. This anatomical distinction may help reconcile our recent finding that spatial neglect is associated with damage to the superior temporal cortex and insula, while others have identified the IPL and TPJ. Specifically, we note that our previous anatomical studies did not use the line bisection task to select neglect patients, while many others used this task. We suggest that anatomical studies that combine patients from both of these two distinct groups may result in misleading findings.

Disturbed line bisection is associated with posterior brain lesions

Neglect patients classically fail to orient and respond to stimuli appearing on their contralesional side. Traditionally, the neglect syndrome has been associated with damage to the right inferior parietal lobule (IPL) and the right temporo-parietal junction (TPJ). Neglect is popularly assessed by two different tasks: line bisection and cancellation. In a previous study (S. Ferber, H.-O. Karnath, How to assess spatial neglect-line bisection or cancellation tasks. J. Clin. Exp. Neuropsychol. 23 (2001) 599–607), we observed that performance on the cancellation task correlates well with the characteristic behavioral disorders used to clinically diagnose spatial neglect, while line bisection was a poor predictor. This might indicate that the disability to correctly bisect lines is a distinct disorder separable from spatial neglect. Here, we assess the anatomy of the patients investigated in that study, and reveal that damage to the temporo-occipital junction correlates with poor performance in the line bisection task. This work extends previous work by Binder et al. (J. Binder, R. Marshall, R. Lazar, J. Benjamin, J.P. Mohr, Distinct syndromes of hemineglect. Arch. Neurol. 49 (1992) 1187–1194) suggesting that line bisection and cancellation identify distinct syndromes. The data suggest that these two tasks dissociate both in terms of behavior and anatomy. This anatomical distinction may help reconcile our recent finding that spatial neglect is associated with damage to the superior temporal cortex and insula, while others have identified the IPL and TPJ. Specifically, we note that our previous anatomical studies did not use the line bisection task to select neglect patients, while many others used this task. We suggest that anatomical studies that combine patients from both of these two distinct groups may result in misleading findings.

Generating animal and tool names: An fMRI study of effective connectivity

The present fMRI study of semantic fluency for animal and tool names provides further evidence for category-specific brain activations, and reports task-related changes in effective connectivity among defined cerebral regions. Two partially segregated systems of functional integration were highlighted: the tool condition was associated with an enhancement of connectivity within left hemispheric regions, including the inferior prefrontal and premotor cortex, the inferior parietal lobule and the temporo-occipital junction; the animal condition was associated with greater coupling among left visual associative regions. These category-specific functional differences extend the evidence for anatomical specialization to lexical search tasks, and provide for the first time evidence of category-specific patterns of functional integration in word-retrieval.