Method matters: an empirical study of impact in cognitive neuroscience

Orbitofrontal contributions to value-based decision making: evidence from humans with frontal lobe damage

The work described here aims to isolate the component processes of decision making that rely critically on particular subregions of the human prefrontal cortex, with a particular focus on the orbitofrontal cortex. Here, experiments isolating specific aspects of decision making, using very simple preference judgment and reinforcement learning paradigms, were carried out in patients with focal frontal damage. The orbitofrontal cortex and the adjacent ventromedial prefrontal cortex play a critical role in decisions based on subjective value, across many categories of stimuli, and in learning to choose between stimuli based on value feedback. However, these regions are not required for learning to choose between actions based on feedback, which instead seems to rely critically on the dorsomedial prefrontal cortex. These results point to a potentially common role for the orbitofrontal cortex in representing the context-sensitive, subjective value of stimuli to allow consistent choices between them. They also argue for multiple, parallel, value-based processes that influence behavior through dissociable mechanisms.

The right hemisphere in esthetic perception

Little about the neuropsychology of art perception and evaluation is known. Most neuropsychological approaches to art have focused on art production and have been anecdotal and qualitative. The field is in desperate need of quantitative methods if it is to advance. Here, we combine a quantitative approach to the assessment of art with modern voxel-lesion-symptom-mapping methods to determine brain–behavior relationships in art perception. We hypothesized that perception of different attributes of art are likely to be disrupted by damage to different regions of the brain. Twenty participants with right hemisphere damage were given the Assessment of Art Attributes, which is designed to quantify judgments of descriptive attributes of visual art. Each participant rated 24 paintings on 6 conceptual attributes (depictive accuracy, abstractness, emotion, symbolism, realism, and animacy) and 6 perceptual attributes (depth, color temperature, color saturation, balance, stroke, and simplicity) and their interest in and preference for these paintings. Deviation scores were obtained for each brain-damaged participant for each attribute based on correlations with group average ratings from 30 age-matched healthy participants. Right hemisphere damage affected participants’ judgments of abstractness, accuracy, and stroke quality. Damage to areas within different parts of the frontal parietal and lateral temporal cortices produced deviation in judgments in four of six conceptual attributes (abstractness, symbolism, realism, and animacy). Of the formal attributes, only depth was affected by inferior prefrontal damage. No areas of brain damage were associated with deviations in interestingness or preference judgments. The perception of conceptual and formal attributes in artwork may in part dissociate from each other and from evaluative judgments. More generally, this approach demonstrates the feasibility of quantitative approaches to the neuropsychology of art.

Performance-based connectivity analysis: a path to convergence with clinical studies

Connectivity analyses have become increasingly important in functional imaging. When used to describe the functional anatomy of a specific behavior, these analyses are generally applied to a subset of the data that demonstrate significant differences when experimental conditions are contrasted. Such data reduction is sub-optimal for a systems approach as it assumes that all data that survive the statistical contrast filter are related to the behavior and that none of the filtered data has a significant function. When such data filtering is applied to speech and language tasks, the resulting functional anatomy rarely reflects the brain lateralization established in over a century and a half of clinical studies. A two-step performance-based connectivity analysis is described in which the first step uses multiple linear regression to establish a direct relationship between regional brain activity and a measure of performance. The second step uses partial correlations to examine the functional relationships between the predictor regions and other brain regions. When applied to regional cerebral blood flow data obtained with positron emission tomography during a speech production task, the results demonstrate left lateralization of motor control areas, thalamic involvement in repetition rate, and auditory cortical suppression, all consistent with clinical observations. The integration of performance measures into the earliest stages of image analysis without reliance on data filtering based on decomposition may provide a path toward convergence with traditional descriptions of functional anatomy based on clinical studies.

Manual, semi-automated, and automated delineation of chronic brain lesions: a comparison of methods

The exact delineation of chronic brain lesions is a crucial step when investigating the relationship between brain structure and (dys-)function. For this, manual tracing, although very time-consuming, is still the gold standard. In order to assess the possible contributions from other methods, we compared manual tracing of lesion boundaries with a newly developed semi-automated and a fully automated approach for lesion definition in a sample of chronic stroke patients (n=11, 5m, median age 12, range 10-30years). Manual tracing requires substantially more human input (4.8-9.6h/subject) than semi-automated (24.9min/subject) and automated processing (1min/subject). When compared with manual tracing as the gold standard, both the semi-automated (tested with 4 different smoothing filters) and the automated approach towards lesion definition performed on an acceptable level, with an average Dice's similarity index of .53-.60 (semi-automated) and .49 (automated processing). In all semi-automated and automated approaches, larger lesions were identified with a significantly higher performance than smaller lesions, as were central versus peripheral voxels, indicating that the surface-to-volume ratio explains this trend. The automated approach failed to identify two lesions. In several cases, indirect lesion effects (such as enlarged ventricles) were detected using the semi-automated or the automated approach. We conclude that manual tracing remains the gold standard for exact lesion delineation, but that semi-automated and automated approaches may be alternatives for larger lesions and/or larger studies. The detection of indirect lesion effects may be another application of such approaches in the future.

Left inferior frontal cortex and syntax: function, structure and behaviour in patients with left hemisphere damage

For the past 150 years, neurobiological models of language have debated the role of key brain regions in language function. One consistently debated set of issues concern the role of the left inferior frontal gyrus in syntactic processing. Here we combine measures of functional activity, grey matter integrity and performance in patients with left hemisphere damage and healthy participants to ask whether the left inferior frontal gyrus is essential for syntactic processing. In a functional neuroimaging study, participants listened to spoken sentences that either contained a syntactically ambiguous or matched unambiguous phrase. Behavioural data on three tests of syntactic processing were subsequently collected. In controls, syntactic processing co-activated left hemisphere Brodmann areas 45/47 and posterior middle temporal gyrus. Activity in a left parietal cluster was sensitive to working memory demands in both patients and controls. Exploiting the variability in lesion location and performance in the patients, voxel-based correlational analyses showed that tissue integrity and neural activity-primarily in left Brodmann area 45 and posterior middle temporal gyrus-were correlated with preserved syntactic performance, but unlike the controls, patients were insensitive to syntactic preferences, reflecting their syntactic deficit. These results argue for the essential contribution of the left inferior frontal gyrus in syntactic analysis and highlight the functional relationship between left Brodmann area 45 and the left posterior middle temporal gyrus, suggesting that when this relationship breaks down, through damage to either region or to the connections between them, syntactic processing is impaired. On this view, the left inferior frontal gyrus may not itself be specialized for syntactic processing, but plays an essential role in the neural network that carries out syntactic computations.

The cognitive neuroscience toolkit for the neuroeconomist: A functional overview

This article provides the beginning neuroeconomist with an introductory overview to the different methods used in human neuroscience. It describes basic strengths and weaknesses of each technique, points to examples of how each technique has been used in neuroeconomic studies, and provides key tutorial references that contain more detailed information. In addition to this overview, the article presents a framework that organizes human neuroscience methods functionally, according to whether they provide tests of the association between brain activity and cognition or behavior, or whether they test the necessity or the sufficiency of brain activity for cognition and behavior. This framework demonstrates the utility of a multi-method research approach, since converging evidence from tests of association, necessity and sufficiency provides the strongest inference regarding brain-behavior relationships. Set against this goal of converging evidence, human neuroscience studies in neuroeconomics currently rely far too heavily on methods that test association, most notably functional MRI.

The neural basis for spatial relations

Studies in semantics traditionally focus on knowledge of objects. By contrast, less is known about how objects relate to each other. In an fMRI study, we tested the hypothesis that the neural processing of categorical spatial relations between objects is distinct from the processing of the identity of objects. Attending to the categorical spatial relations compared with attending to the identity of objects resulted in greater activity in superior and inferior parietal cortices (especially on the left) and posterior middle frontal cortices bilaterally. In an accompanying lesion study, we tested the hypothesis that comparable areas would be necessary to represent categorical spatial relations and that the hemispheres differ in their biases to process categorical or coordinate spatial relations. Voxel-based lesion symptom mapping results were consistent with the fMRI observations. Damage to a network comprising left inferior frontal, supramarginal, and angular gyri resulted in behavioral impairment on categorical spatial judgments. Homologous right brain damage also produced such deficits, albeit less severely. The reverse pattern was observed for coordinate spatial processing. Right brain damage to the middle temporal gyrus produced more severe deficits than left hemisphere damage. Additional analyses suggested that some areas process both kinds of spatial relations conjointly and others distinctly. The left angular and inferior frontal gyrus processes coordinate spatial information over and above the categorical processing. The anterior superior temporal gyrus appears to process categorical spatial information uniquely. No areas within the right hemisphere processed categorical spatial information uniquely. Taken together, these findings suggest that the functional neuroanatomy of categorical and coordinate processing is more nuanced than implied by a simple hemispheric dichotomy.

Anterior temporal involvement in semantic word retrieval: voxel-based lesion-symptom mapping evidence from aphasia

Analysis of error types provides useful information about the stages and processes involved in normal and aphasic word production. In picture naming, semantic errors (horse for goat) generally result from something having gone awry in lexical access such that the right concept was mapped to the wrong word. This study used the new lesion analysis technique known as voxel-based lesion-symptom mapping to investigate the locus of lesions that give rise to semantic naming errors. Semantic errors were obtained from 64 individuals with post-stroke aphasia, who also underwent high-resolution structural brain scans. Whole brain voxel-based lesion-symptom mapping was carried out to determine where lesion status predicted semantic error rate. The strongest associations were found in the left anterior to mid middle temporal gyrus. This area also showed strong and significant effects in further analyses that statistically controlled for deficits in pre-lexical, conceptualization processes that might have contributed to semantic error production. This study is the first to demonstrate a specific and necessary role for the left anterior temporal lobe in mapping concepts to words in production. We hypothesize that this role consists in the conveyance of fine-grained semantic distinctions to the lexical system. Our results line up with evidence from semantic dementia, the convergence zone framework and meta-analyses of neuroimaging studies on word production. At the same time, they cast doubt on the classical linkage of semantic error production to lesions in and around Wernicke's area.

Cerebral localization of functions and the neurology of language: fact versus fiction or is it something else?

Over the last 15 years there has been a burgeoning number of publications using functional brain imaging (>40,000 articles based on an ISI/Web of Science search) to localize behavioral and cognitive processes to specific areas in the human brain that are often not confirmed by traditional, lesion-based studies. Thus, there is a need to reassess what cerebral localization of functions is and is not. Otherwise, there is no rational way to interpret the escalating claims of localization in the functional imaging literature that is taking on the appearance of neurophysiologic "phrenology". This article will present arguments to suggest that functional localization in the brain is a robust but very dynamic, four-dimensional process. It is a learned phenomenon driven over time by large-scale, spatially distributed, neural networks seeking to efficiently maximize the processing, storage, and manipulation of information for cognitive and behavioral operations. Because of historical considerations and space limitations, the main focus will be on localization of language-related functions whose theoretical neurological basis can be generalized for any complex cognitive-behavioral function.

Lesion evidence that two distinct regions within prefrontal cortex are critical for n-back performance in humans

Although prefrontal cortex is clearly important in executive function, the specific processes carried out by particular regions within human prefrontal cortex remain a matter of debate. A rapidly growing corpus of functional imaging work now implicates various areas within prefrontal cortex in a wide range of "executive" tasks. Loss-of-function studies can help constrain the interpretation of such evidence by testing to what extent particular brain areas are necessary for a given cognitive process. Here we apply a component process analysis to understand prefrontal contributions to the n-back task, a widely used test of working memory, in a cohort of patients with focal prefrontal damage. We investigated letter 2-back task performance in 27 patients with focal damage to various regions within prefrontal cortex, compared to 29 demographically matched control subjects. Both "behavior-defined" approaches, using qualitative lesion analyses and voxel-based lesion-symptom mapping methods, and more conventional "lesion-defined" groupwise comparisons were undertaken to determine the relationships between specific sites of damage within prefrontal cortex and particular aspects of n-back task performance. We confirmed a critical role for left lateral prefrontal cortex in letter 2-back performance. We also identified a critical role for medial prefrontal cortex in this task: Damage to dorsal anterior cingulate cortex and adjacent dorsal fronto-medial cortex led to a pattern of impairment marked by high false alarm rates, distinct from the impairment associated with lateral prefrontal damage. These findings provide converging support for regionally specific models of human prefrontal function.

Left inferior frontal gyrus is critical for response inhibition

Background

Lesion studies in human and non-human primates have linked several different regions of prefrontal cortex (PFC) with the ability to inhibit inappropriate motor responses. However, recent functional neuroimaging studies have specifically implicated right inferior PFC in response inhibition. Right frontal dominance for inhibitory motor control has become a commonly accepted view, although support for this position has not been consistent. Particularly conspicuous is the lack of data on the importance of the homologous region in the left hemisphere. To investigate whether the left inferior frontal gyrus (IFG) is critical for response inhibition, we used neuropsychological methodology with carefully characterized brain lesions in neurological patients.

Results

Twelve individuals with damage in the left IFG and the insula were tested in a Go/NoGo response inhibition task. In alternating blocks, the difficulty of response inhibition was easy (50% NoGo trials) or hard (10% NoGo trials). Controls showed the predicted pattern of faster reaction times and more false alarm errors in the hard condition. Left IFG patients had higher error rates than controls in both conditions, but were more impaired in the hard condition, when a greater degree of inhibitory control was required. In contrast, a patient control group with orbitofrontal cortex lesions showed intact performance.

Conclusion

Recent neuroimaging studies have focused on a highly specific association between right IFG and inhibitory control. The present results indicate that the integrity of left IFG is also critical for successful implementation of inhibitory control over motor responses. Our findings demonstrate the importance of obtaining converging evidence from multiple methodologies in cognitive neuroscience.

An evaluation of traditional and novel tools for lesion behavior mapping

Kinkingnéhun et al. (Kinkingnéhun, S., Volle, E., Pélégrini-Issac, M., Golmard, J.L., Lehéricy, S., du Boisguéheneuc, F., Zhang-Nunes, S., Sosson, D., Duffau, H., Samson, Y., Levy, R., Dubois, B., 2007. A novel approach to clinical-radiological correlations: Anatomo-Clinical Overlapping Maps (AnaCOM): method and validation. NeuroImage 37: 1237-1249.) have recently described a novel approach for lesion-behavior mapping (LBM), referred to as Anatomo-Clinical Overlapping Maps (AnaCOM). Conventional voxelwise LBM tools apply statistics to contrast behavioral performance of patients with lesions that encompass given voxels to control patients where these voxels are spared. In contrast, AnaCOM contrasts performance of patients with injury involving given voxels to the performance of neurologically healthy participants. The authors correctly note that their procedure can offer substantially more statistical power than conventional LBM methods. We compared AnaCOM to conventional LBM techniques by examining hemiparesis (a common consequence of stroke) as the behavior of interest. We found that AnaCOM detected many regions of the middle cerebral artery territory not associated with the motor system. We suggest that conventional LBM techniques detect regions that are damaged in patients with a deficit while spared in those without a deficit, while AnaCOM detects regions that are associated with a deficit. Therefore, this new measure may offer poor specificity. Furthermore, on theoretical grounds we suggest that permutation-based thresholding will be a more sensitive method for controlling familywise error than the method of counting lesion-overlap clusters used by AnaCOM. Finally, we note that the within group variability tends to be smaller for neurologically healthy controls than in neurological patients, due to ceiling effects. Therefore, we suggest that nonparametric measures or the Welch's t-test are more appropriate than the conventional pooled variance t-test used by AnaCOM.

Evaluating frontal and parietal contributions to spatial working memory with repetitive transcranial magnetic stimulation

Functional neuroimaging studies have produced contradictory data about the extent to which specific regions of the frontal and the posterior parietal cortices contribute to the retention of information in spatial working memory. We used high frequency repetitive transcranial magnetic stimulation (rTMS) to assess the necessity for the short-term retention of spatial information of brain areas identified by previous functional imaging studies: dorsolateral prefrontal cortex (dlPFC), frontal eye fields (FEF), superior parietal lobule (SPL) and intraparietal sulcus (IPS). 10 Hz rTMS spanned the 3-s delay period of a spatial delayed-recognition task. The postcentral gyrus (PCG) was included to control for any regionally non-specific effects of rTMS. The only regionally-specific effect was a significant decrease in reaction time when rTMS was applied to SPL. Additionally, rTMS lowered accuracy to a greater extent when applied to left than to right hemisphere, and was more disruptive when applied contralaterally vs. ipsilaterally to the visual field in which the memory probe was presented. Although seemingly paradoxical, the finding of rTMS-induced improvement in task performance has a precedent, and is consistent with the idea that regions associated with spatial sensory-motor processing make necessary contributions to the short-term retention of this information. Possible factors underlying rTMS-induced behavioral facilitation are considered.

Patient Registries in Cognitive Neuroscience Research: Advantages, Challenges, and Practical Advice

Neuropsychological work is the historical foundation of cognitive neuroscience and continues to be an important method in the study of the neural basis of human behavior, complementing newer techniques for investigating brain structure-function relationships in human subjects. Recent advances in neuroimaging, statistics and information management provide powerful tools to support neuropsychological research. At the same time, changing ethical requirements and privacy concerns impose increasingly high standards on the procedures used to recruit research participants, and on subsequent data management. Shared, centrally managed research registries provide a framework for facilitating access to this method for nonclinicians, addressing ethical concerns, streamlining recruitment and screening procedures, and coordinating subsequent research contacts and data storage. We report the experience of two such registries: the patient database of the Center for Cognitive Neuroscience at the University of Pennsylvania, and the Cognitive Neuroscience Research Registry at McGill University.

Speech and language functions that require a functioning Broca's area

A number of previous studies have indicated that Broca's area has an important role in understanding and producing syntactically complex sentences and other language functions. If Broca's area is critical for these functions, then either infarction of Broca's area or temporary hypoperfusion within this region should cause impairment of these functions, at least while the neural tissue is dysfunctional. The opportunity to identify the language functions that depend on Broca's area in a particular individual was provided by a patient with hyperacute stroke who showed selective hypoperfusion, with minimal infarct, in Broca's area, and acutely impaired production of grammatical sentences, comprehension of semantically reversible (but not non-reversible) sentences, spelling, and motor planning of speech articulation. When blood flow was restored to Broca's area, as demonstrated by repeat perfusion weighted imaging, he showed immediate recovery of these language functions. The identification of language functions that were impaired when Broca's area was dysfunctional (due to low blood flow) and recovered when Broca's area was functional again, provides evidence for the critical role of Broca's area in these language functions, at least in this individual.

Neural regions essential for reading and spelling of words and pseudowords

OBJECTIVE

To identify dysfunctional brain regions critical for impaired reading/spelling of words/pseudowords by evaluating acute stroke patients on lexical tests and magnetic resonance imaging, before recovery or reorganization of structure-function relationships.

METHODS

A series of 106 consenting patients were administered oral reading and spelling tests within 24 hours of left supratentorial stroke onset. Patients underwent diffusion- and perfusion-weighted magnetic resonance examination the same day to identify regions of hypoperfusion/infarct of 16 Brodmann areas.

RESULTS

Simultaneous logistic regression analysis demonstrated that dysfunction of left Brodmann areas 40 (supramarginal gyrus) and 37 (posterior-inferior temporal/fusiform gyrus) best predicted impairment in reading words (odds ratio [OR], 6.20 [95% confidence interval (CI), 1.54-24.96] and 2.71 [95% CI, 0.87-8.45], respectively), reading pseudowords (OR, 39.65 [95% CI 3.9-400.78] and 4.41 [95% CI, 1.1-17.51], respectively), spelling words (OR, 14.11 [95% CI 1.37-144.93] and 7.41 [95% CI, 1.48-37.24], respectively), and spelling pseudowords (OR, 4.84 [95% CI, 0.73-32.13] and 7.74 [95% CI, 1.56-38.51], respectively). Whole-brain voxel-wise analyses demonstrated voxel clusters within these regions that were most strongly associated with task deficits.

INTERPRETATION

Results indicate that a shared network of regions including parts of left Brodmann areas 37 and 40 is necessary for reading and spelling of words and pseudowords. Further studies may define the precise roles of these brain regions in language. Identification of any neural regions specific to one of these tasks or one type of stimuli will require study of more patients with selective deficits.

Retrieval of emotional memories

Long-term memories are influenced by the emotion experienced during learning as well as by the emotion experienced during memory retrieval. The present article reviews the literature addressing the effects of emotion on retrieval, focusing on the cognitive and neurological mechanisms that have been revealed. The reviewed research suggests that the amygdala, in combination with the hippocampus and prefrontal cortex, plays an important role in the retrieval of memories for emotional events. The neural regions necessary for online emotional processing also influence emotional memory retrieval, perhaps through the reexperience of emotion during the retrieval process.

Power in Voxel-based lesion-symptom mapping

Lesion analysis in brain-injured populations complements what can be learned from functional neuroimaging. Voxel-based approaches to mapping lesion-behavior correlations in brain-injured populations are increasingly popular, and have the potential to leverage image analysis methods drawn from functional magnetic resonance imaging. However, power is a major concern for these studies, and is likely to vary regionally due to the distribution of lesion locations. Here, we outline general considerations for voxel-based methods, characterize the use of a nonparametric permutation test adapted from functional neuroimaging, and present methods for regional power analysis in lesion studies.

The Parieto-Frontal Integration Theory (P-FIT) of intelligence: converging neuroimaging evidence

"Is there a biology of intelligence which is characteristic of the normal human nervous system?" Here we review 37 modern neuroimaging studies in an attempt to address this question posed by Halstead (1947) as he and other icons of the last century endeavored to understand how brain and behavior are linked through the expression of intelligence and reason. Reviewing studies from functional (i.e., functional magnetic resonance imaging, positron emission tomography) and structural (i.e., magnetic resonance spectroscopy, diffusion tensor imaging, voxel-based morphometry) neuroimaging paradigms, we report a striking consensus suggesting that variations in a distributed network predict individual differences found on intelligence and reasoning tasks. We describe this network as the Parieto-Frontal Integration Theory (P-FIT). The P-FIT model includes, by Brodmann areas (BAs): the dorsolateral prefrontal cortex (BAs 6, 9, 10, 45, 46, 47), the inferior (BAs 39, 40) and superior (BA 7) parietal lobule, the anterior cingulate (BA 32), and regions within the temporal (BAs 21, 37) and occipital (BAs 18, 19) lobes. White matter regions (i.e., arcuate fasciculus) are also implicated. The P-FIT is examined in light of findings from human lesion studies, including missile wounds, frontal lobotomy/leukotomy, temporal lobectomy, and lesions resulting in damage to the language network (e.g., aphasia), as well as findings from imaging research identifying brain regions under significant genetic control. Overall, we conclude that modern neuroimaging techniques are beginning to articulate a biology of intelligence. We propose that the P-FIT provides a parsimonious account for many of the empirical observations, to date, which relate individual differences in intelligence test scores to variations in brain structure and function. Moreover, the model provides a framework for testing new hypotheses in future experimental designs.

Improving Lesion-Symptom Mapping

Measures of brain activation (e.g., changes in scalp electrical potentials) have become the most popular method for inferring brain function. However, examining brain disruption (e.g., examining behavior after brain injury) can complement activation studies. Activation techniques identify regions involved with a task, whereas disruption techniques are able to discover which regions are crucial for a task. Voxel-based lesion mapping can be used to determine relationships between behavioral measures and the location of brain injury, revealing the function of brain regions. Lesion mapping can also correlate the effectiveness of neurosurgery with the location of brain resection, identifying optimal surgical targets. Traditionally, voxel-based lesion mapping has employed the chi-square test when the clinical measure is binomial and the Student's t test when measures are continuous. Here we suggest that the Liebermeister approach for binomial data is more sensitive than the chi-square test. We also suggest that a test described by Brunner and Munzel is more appropriate than the t test for nonbinomial data because clinical and neuropsychological data often violate the assumptions of the t test. We test our hypotheses comparing statistical tests using both simulated data and data obtained from a sample of stroke patients with disturbed spatial perception. We also developed software to implement these tests (MRIcron), made freely available to the scientific community.

Neural networks essential for naming and word comprehension

Lesion/deficit association studies of aphasia commonly focus on one brain region as primarily responsible for a particular language deficit. However, functional imaging and some lesion studies indicate that multiple brain regions are likely necessary for any language task. We tested 156 acute stroke patients on basic language tasks (naming and spoken and written word comprehension) and magnetic resonance diffusion and perfusion imaging to determine the relative contributions of various brain regions to each task. Multivariate linear regression analysis indicated that the error rate on each task was best predicted by dysfunction in several perisylvian regions, with both common and distinct regions for the 3 tasks.

The contribution of neuroimaging to the study of language and aphasia

New structural and functional imaging methods continue to be developed at a rapid pace. In the last 25 years, advanced imaging techniques have provided insights into how language is represented and processed in the brain and how it can be disrupted by damage to, or dysfunction of, various parts of the brain. Imaging studies have also yielded new information regarding how individuals recover language after stroke. We briefly review the strengths and weaknesses of the various radiological methods currently used to study language and aphasia.

The Human Striatum is Necessary for Responding to Changes in Stimulus Relevance

Various lines of evidence suggest that the striatum is implicated in cognitive flexibility. The neuropsychological evidence has, for the most part, been based on research with patients with Parkinson's disease, which is accompanied by chemical disruption of both the striatum and the prefrontal cortex. The present study examined this issue by testing patients with focal lesions of the striatum on a task measuring two forms of cognitive switching. Patients with striatal, but not frontal lobe lesions, were impaired in switching between concrete sensory stimuli. By contrast, both patient groups were unimpaired when switching between abstract task rules relative to baseline nonswitch trials. These results reveal a dissociation between two distinct forms of cognitive f lexibility, providing converging evidence for a role of the striatum in f lexible control functions associated with the selection of behaviorally relevant stimuli.

Neuroimaging in late-life depression

Late-life depression may be associated with vasculopathy. Neuroimaging has been a critical tool in exploring the relationship between this form of depression and vascular factors. Magnetic resonance imaging has been the most widely used tool, but there is potential to use other structural imaging techniques as well as functional neuroimaging methodologies. Neuroimaging may potentially be utilized at some point as a biomarker for late-life depression, thus helping with diagnosis and guiding treatment.

Restoring cerebral blood flow reveals neural regions critical for naming

We identified areas of the brain that are critical for naming pictures of objects, using a new methodology for testing which components of a network of brain regions are essential for that task. We identified areas of hypoperfusion and structural damage with magnetic resonance perfusion- and diffusion-weighted imaging immediately after stroke in 87 individuals with impaired picture naming. These individuals were reimaged after 3-5 d, after a subset of patients underwent intervention to restore normal blood flow, to determine areas of the brain that had reperfused. We identified brain regions in which reperfusion was associated with improvement in picture naming. Restored blood flow to left posterior middle temporal/fusiform gyrus, Broca's area, and/or Wernicke's area accounted for most acute improvement after stroke. Results show that identifying areas of reperfusion that are associated with acute improvement of a function can reveal the brain regions essential for that function.

Does functional neuroimaging solve the questions of neurolinguistics?

Neurolinguistic research has been engaged in evaluating models of language using measures from brain structure and function, and/or in investigating brain structure and function with respect to language representation using proposed models of language. While the aphasiological strategy, which classifies aphasias based on performance modality and a few linguistic variables, has been the most stable, cognitive neurolinguistics has had less success in reliably associating more elaborately proposed levels and units of language models with brain structure. Functional imaging emerged at this stage of neurolinguistic research. In this review article, it is proposed that the often-inconsistent superfluity of outcomes arising from functional imaging studies of language awaits adjustment at both "ends" of the process: model and data. Assumptions that our current language models consistently and reliably represent implicit knowledge within human cerebral processing are in line for major revision; and the promise of functional brain imaging to reveal any such knowledge structures must incorporate stable correlates of the imaging signal as dependent variable.

Dissociation between emotion and personality judgments: Convergent evidence from functional neuroimaging

Cognitive neuroscientists widely agree on the importance of providing convergent evidence from neuroimaging and lesion studies to establish structure-function relationships. However, such convergent evidence is, in practice, rarely provided. A previous lesion study found a striking double dissociation between two superficially similar social judgment processes, emotion recognition and personality attribution, based on the same body movement stimuli (point-light walkers). Damage to left frontal opercular (LFO) cortices was associated with impairments in personality trait attribution, whereas damage to right postcentral/supramarginal cortices was associated with impairments in emotional state attribution. Here, we present convergent evidence from fMRI in support of this double dissociation, with regions of interest (ROIs) defined by the regions of maximal lesion overlap from the previous study. Subjects learned four emotion words and four trait words, then watched a series of short point-light walker body movement stimuli. After each stimulus, subjects saw either an emotion word or a trait word and rated how well the word described the stimulus. The LFO ROI exhibited greater activity during personality judgments than during emotion judgments. In contrast, the right postcentral/supramarginal ROI exhibited greater activity during emotion judgments than during personality judgments. Follow-up experiments ruled out the possibility that the LFO activation difference was due to word frequency differences. Additionally, we found greater activity in a region of the medial prefrontal cortex previously associated with "theory of mind" tasks when subjects made personality, as compared to emotion judgments.