Study design and methods: U.S. study to protect brain health through lifestyle intervention to reduce risk (U.S. POINTER)

INTRODUCTION

The U.S. study to protect brain health through lifestyle intervention to reduce risk (U.S. POINTER) is conducted to confirm and expand the results of the Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER) in Americans.

METHODS

U.S. POINTER was planned as a 2-year randomized controlled trial of two lifestyle interventions in 2000 older adults at risk for dementia due to well-established factors. The primary outcome is a global cognition composite that permits harmonization with FINGER.

RESULTS

U.S. POINTER is centrally coordinated and conducted at five clinical sites (ClinicalTrials.gov: NCT03688126). Outcomes assessments are completed at baseline and every 6 months. Both interventions focus on exercise, diet, cognitive/social stimulation, and cardiovascular health, but differ in intensity and accountability. The study partners with a worldwide network of similar trials for harmonization of methods and data sharing.

DISCUSSION

U.S. POINTER is testing a potentially sustainable intervention to support brain health and Alzheimer's prevention for Americans. Impact is strengthened by the targeted participant diversity and expanded scientific scope through ancillary studies.

Optimizing quantification of MK6240 tau PET in unimpaired older adults

Accurate measurement of Alzheimer's disease (AD) pathology in older adults without significant clinical impairment is critical to assessing intervention strategies aimed at slowing AD-related cognitive decline. The U.S. Study to Protect Brain Health Through Lifestyle Intervention to Reduce Risk (POINTER) is a 2-year randomized controlled trial to evaluate the effect of multicomponent risk reduction strategies in older adults (60-79 years) who are cognitively unimpaired but at increased risk for cognitive decline/dementia due to factors such as cardiovascular disease and family history. The POINTER Imaging ancillary study is collecting tau-PET ([18F]MK6240), beta-amyloid (Aβ)-PET ([18F]florbetaben [FBB]) and MRI data to evaluate neuroimaging biomarkers of AD and cerebrovascular pathophysiology in this at-risk sample. Here 481 participants (70.0±5.0; 66% F) with baseline MK6240, FBB and structural MRI scans were included. PET scans were coregistered to the structural MRI which was used to create FreeSurfer-defined reference regions and target regions of interest (ROIs). We also created off-target signal (OTS) ROIs to examine the magnitude and distribution of MK6240 OTS across the brain as well as relationships between OTS and age, sex, and race. OTS was unimodally distributed, highly correlated across OTS ROIs and related to younger age and sex but not race. Aiming to identify an optimal processing approach for MK6240 that would reduce the influence of OTS, we compared our previously validated MRI-guided standard PET processing and 6 alternative approaches. The alternate approaches included combinations of reference region erosion and meningeal OTS masking before spatial smoothing as well as partial volume correction. To compare processing approaches we examined relationships between target ROIs (entorhinal cortex (ERC), hippocampus or a temporal meta-ROI (MetaROI)) SUVR and age, sex, race, Aβ and a general cognitive status measure, the Modified Telephone Interview for Cognitive Status (TICSm). Overall, the processing approaches performed similarly, and none showed a meaningful improvement over standard processing. Across processing approaches we observed previously reported relationships with MK6240 target ROIs including positive associations with age, an Aβ+> Aβ- effect and negative associations with cognition. In sum, we demonstrated that different methods for minimizing effects of OTS, which is highly correlated across the brain within subject, produced no substantive change in our performance metrics. This is likely because OTS contaminates both reference and target regions and this contamination largely cancels out in SUVR data. Caution should be used when efforts to reduce OTS focus on target or reference regions in isolation as this may exacerbate OTS contamination in SUVR data.

U.S. POINTER: Lessons learned about delivery of a multi‐domain lifestyle intervention during the COVID‐19 pandemic

Background

U.S. POINTER is testing whether multidomain lifestyle interventions focused on physical exercise, nutrition, cognitive challenge, and risk factor management reduces risk of cognitive decline in a heterogeneous population of at‐risk older adults in America. The study adapts the FINGER (Finnish Intervention Geriatric Study to Prevent Cognitive Impairment and Disability) interventions to fit the United States culture and delivers the intervention within the community at 5 sites across the country.

Method

U.S. POINTER is a 2‐year RCT that will enroll 2000 cognitively unimpaired older adults who are at risk for cognitive decline due sedentary lifestyle, poor diet and other factors. Participants are randomized to one of two lifestyle intervention groups that differ in format and intensity. In 2020, the COVID‐19 pandemic presented a number of challenges for the study that affected recruitment, assessment schedules, and intervention delivery.

Result

As of March 2020, when COVID‐19 incidence was on an exponential rise in the US, 240 participants had been enrolled in U.S. POINTER. In response to local and national safety mandates, study activities were paused from March 23^rd to July 13^th. During the pause, sites remained in contact with study candidates and enrolled participants to provide ongoing support to keep them engaged in the trial. Enrollees also received regular telephone calls to encourage continued adherence to their assigned lifestyle intervention. In response to the multiple pandemic‐related challenges, study protocols and procedures were adapted to facilitate and encourage participant adherence to intervention activities. At study re‐start, retention was 98%. Despite climbing COVID‐19 infection rates nationwide, enrollment at all 5 sites has continued at a steady rate (N=540 as of Jan2021), virtual Team Meeting attendance for both lifestyle groups exceeds 80%, and participants continue to successfully work toward their intervention goals.

Conclusion

The COVID‐19 pandemic presented unprecedented challenges, but it also provided a unique opportunity to adapt intervention delivery so that a nonpharmacological community‐based trial could continue – even during a debilitating global health crisis. U.S. POINTER’s adaptations to pandemic‐related challenges may ultimately increase the resilience of its interventions to even the most challenging of circumstances that older adults will face now and in the future.

Cognitive Impairment in Aging Physicians: Current Challenges and Possible Solutions

Aging physicians are at a higher risk of cognitive impairment, undermining patient safety and unraveling physicians' careers. Neurologists, occupational health physicians, and psychiatrists will participate in both health system policy decisions and individual patient evaluations. We address cognitive impairment in aging physicians and attendant risks and benefits. If significant cognitive impairment is found after an appropriate evaluation, precautions to confidentially support physicians' practicing safely for as long as possible should be instituted. Understanding that there is heterogeneity and variability in the course of cognitive disorders is crucial to supporting cognitively impaired, practicing physicians. Physicians who are no longer able to practice clinically have other meaningful options.

Neural Connectivity in Syntactic Movement Processing

Linguistic theory suggests non-canonical sentences subvert the dominant agent-verb-theme order in English via displacement of sentence constituents to argument (NP-movement) or non-argument positions (wh-movement). Both processes have been associated with the left inferior frontal gyrus and posterior superior temporal gyrus, but differences in neural activity and connectivity between movement types have not been investigated. In the current study, functional magnetic resonance imaging data were acquired from 21 adult participants during an auditory sentence-picture verification task using passive and active sentences contrasted to isolate NP-movement, and object- and subject-cleft sentences contrasted to isolate wh-movement. Then, functional magnetic resonance imaging data from regions common to both movement types were entered into a dynamic causal modeling analysis to examine effective connectivity for wh-movement and NP-movement. Results showed greater left inferior frontal gyrus activation for Wh > NP-movement, but no activation for NP > Wh-movement. Both types of movement elicited activity in the opercular part of the left inferior frontal gyrus, left posterior superior temporal gyrus, and left medial superior frontal gyrus. The dynamic causal modeling analyses indicated that neither movement type significantly modulated the connection from the left inferior frontal gyrus to the left posterior superior temporal gyrus, nor vice-versa, suggesting no connectivity differences between wh- and NP-movement. These findings support the idea that increased complexity of wh-structures, compared to sentences with NP-movement, requires greater engagement of cognitive resources via increased neural activity in the left inferior frontal gyrus, but both movement types engage similar neural networks.

Neuropathology of Autosomal Dominant Alzheimer Disease in the National Alzheimer Coordinating Center Database

Alzheimer disease (AD) represents a genetically heterogeneous entity. To elucidate neuropathologic features of autosomal dominant AD ([ADAD] due to PSEN1, APP, or PSEN2 mutations), we compared hallmark AD pathologic findings in 60 cases of ADAD and 120 cases of sporadic AD matched for sex, race, ethnicity, and disease duration. Greater degrees of neuritic plaque and neurofibrillary tangle formation and cerebral amyloid angiopathy (CAA) were found in ADAD (p values < 0.01). Moderate to severe CAA was more prevalent in ADAD (63.3% vs. 39.2%, p = 0.003), and persons with PSEN1 mutations beyond codon 200 had higher average Braak scores and severity and prevalence of CAA than those with mutations before codon 200. Lewy body pathology was less extensive in ADAD but was present in 27.1% of cases. We also describe a novel pathogenic PSEN1 mutation (P267A). The finding of more severe neurofibrillary pathology and CAA in ADAD, particularly in carriers of PSEN1 mutations beyond codon 200, warrants consideration when designing trials to treat or prevent ADAD. The finding of Lewy body pathology in a substantial minority of ADAD cases supports the assertion that development of Lewy bodies may be in part driven by abnormal β-amyloid protein precursor processing.

Effects of acute levodopa challenge on resting cerebral blood flow in Parkinson's Disease patients assessed using pseudo-continuous arterial spin labeling

Introduction. Levodopa is the gold-standard for treatment of Parkinson’s disease (PD) related motor symptoms. In this study, we used pseudo-continuous arterial spin labeling (pCASL) to quantify changes in cerebral blood flow (CBF) after acute oral administration of levodopa in PD patients.

Materials and Methods. Thirteen patients (3 females, age 66.2 ± 8.7 years) with moderately advanced PD (Hoehn and Yahr stage >2 (median 2.5), disease duration >3 years) were scanned on a 3T Siemens MR scanner before and after oral levodopa administration. Statistical parametric mapping was used to detect drug-induced changes in CBF and its correlation to clinical severity scales. Images were normalized and flipped in order to examine effects on the more affected (left) and less affected (right) cerebral hemispheres across the cohort.

Results. Levodopa did not change global CBF but increased regional CBF in dorsal midbrain, precuneus/cuneus, more affected inferior frontal pars opercularis and triangularis, bilateral pre- and postcentral gyri, more affected inferior parietal areas, as well as less affected putamen/globus pallidus by 27–74% (p < 0.05, FWE corrected for multiple comparisons). CBF change was negatively correlated with improvement in bradykinesia UPDRS-III subscore in the more affected precentral gyrus, and total predrug UPDRS-III score in the mid-cingulate region. Drug-induced CBF change in a widespread network of regions including parietal and postcentral areas was also negatively correlated with the predrug rigidity UPDRS-III subscore.

Conclusion. These findings are in line with prior reports of abnormal activity in the nigrostriatal pathway of PD patients and demonstrate the feasibility of pCASL as a neuroimaging tool for investigating in vivo physiological effects of acute drug administration in PD.

Olfactory-visual integration facilitates perception of subthreshold negative emotion

A fast growing literature of multisensory emotion integration notwithstanding, the chemical senses, intimately associated with emotion, have been largely overlooked. Moreover, an ecologically highly relevant principle of "inverse effectiveness", rendering maximal integration efficacy with impoverished sensory input, remains to be assessed in emotion integration. Presenting minute, subthreshold negative (vs. neutral) cues in faces and odors, we demonstrated olfactory-visual emotion integration in improved emotion detection (especially among individuals with weaker perception of unimodal negative cues) and response enhancement in the amygdala. Moreover, while perceptual gain for visual negative emotion involved the posterior superior temporal sulcus/pSTS, perceptual gain for olfactory negative emotion engaged both the associative olfactory (orbitofrontal) cortex and amygdala. Dynamic causal modeling (DCM) analysis of fMRI timeseries further revealed connectivity strengthening among these areas during crossmodal emotion integration. That multisensory (but not low-level unisensory) areas exhibited both enhanced response and region-to-region coupling favors a top-down (vs. bottom-up) account for olfactory-visual emotion integration. Current findings thus confirm the involvement of multisensory convergence areas, while highlighting unique characteristics of olfaction-related integration. Furthermore, successful crossmodal binding of subthreshold aversive cues not only supports the principle of "inverse effectiveness" in emotion integration but also accentuates the automatic, unconscious quality of crossmodal emotion synthesis.

Diffusion imaging of nigral alterations in early Parkinson's disease with dopaminergic deficits

BACKGROUND

This study reports the baseline characteristics of diffusion tensor imaging data in Parkinson's disease (PD) patients and healthy control subjects from the Parkinson's Progression Markers Initiative. The main goals were to replicate previous findings of abnormal diffusion imaging values from the substantia nigra. in a large multicenter cohort and determine whether nigral diffusion alterations are associated with dopamine deficits.

METHODS

Two hundred twenty subjects (PD = 153; control = 67) from 10 imaging sites were included. All subjects had a full neurological exam, a ((123) I)ioflupane dopamine transporter (DAT) single-photon emission computer tomography scan, and diffusion tensor imaging. Fractional anisotropy as well as radial and axial diffusivity was computed within multiple regions across the substantia nigra.

RESULTS

A repeated-measures analysis of variance found a marginally nonsignificant interaction between regional fractional anisotropy of the substantia nigra and disease status (P = 0.08), conflicting with an earlier study. However, a linear mixed model that included control regions in addition to the nigral regions revealed a significant interaction between regions and disease status (P = 0.002), implying a characteristic distribution of reduced fractional anisotropy across the substantia nigra in PD. Reduced fractional anisotropy in PD was also associated with diminished DAT binding ratios. Both axial and radial diffusivity were also abnormal in PD.

CONCLUSIONS

Although routine nigral measurements of fractional anisotropy are clinically not helpful, the findings in this study suggest that more-sophisticated diffusion imaging protocols should be used when exploring the clinical utility of this imaging modality.

Improving clinical cognitive testing: report of the AAN Behavioral Neurology Section Workgroup

OBJECTIVE

To evaluate the evidence basis of single-domain cognitive tests frequently used by behavioral neurologists in an effort to improve the quality of clinical cognitive assessment.

METHODS

Behavioral Neurology Section members of the American Academy of Neurology were surveyed about how they conduct clinical cognitive testing, with a particular focus on the Neurobehavioral Status Exam (NBSE). In contrast to general screening cognitive tests, an NBSE consists of tests of individual cognitive domains (e.g., memory or language) that provide a more comprehensive diagnostic assessment. Workgroups for each of 5 cognitive domains (attention, executive function, memory, language, and spatial cognition) conducted evidence-based reviews of frequently used tests. Reviews focused on suitability for office-based clinical practice, including test administration time, accessibility of normative data, disease populations studied, and availability in the public domain.

RESULTS

Demographic and clinical practice data were obtained from 200 respondents who reported using a wide range of cognitive tests. Based on survey data and ancillary information, between 5 and 15 tests in each cognitive domain were reviewed. Within each domain, several tests are highlighted as being well-suited for an NBSE.

CONCLUSIONS

We identified frequently used single-domain cognitive tests that are suitable for an NBSE to help make informed choices about clinical cognitive assessment. Some frequently used tests have limited normative data or have not been well-studied in common neurologic disorders. Utilizing standardized cognitive tests, particularly those with normative data based on the individual's age and educational level, can enhance the rigor and utility of clinical cognitive assessment.

Brain morphometric changes associated with childhood-onset systemic lupus erythematosus and neurocognitive deficit

OBJECTIVE

To use structural magnetic resonance imaging (MRI) to characterize changes in gray matter and white matter volumes between patients with childhood-onset systemic lupus erythematosus (SLE) and matched controls, between patients with childhood-onset SLE with and those without neurocognitive deficit, and in relation to disease duration and treatment with steroids.

METHODS

Twenty-two patients with childhood-onset SLE and 19 healthy controls underwent high-resolution structural MRI. Probability density maps for gray matter and white matter were compared between groups.

RESULTS

Neuropsychological testing confirmed the presence of neurocognitive deficit in 8 patients with childhood-onset SLE. Multiple brain regions had reduced gray matter volume in the patients with childhood- onset SLE with neurocognitive deficit versus controls or patients with childhood-onset SLE without neurocognitive deficit. Neither disease duration nor cumulative oral or intravenous steroid doses accounted for decreases in gray matter. White matter volume was also reduced in patients with childhood-onset SLE with neurocognitive deficit, and the reduction was positively associated with both disease duration and cumulative oral steroid dose. Conversely, higher cumulative intravenous steroid doses were associated with higher white matter volumes.

CONCLUSION

Neurocognitive deficit in patients with childhood-onset SLE is associated with multifocal decreases in both gray and white matter volumes. Since only white matter volume changes are related to disease duration and cumulative oral steroid use, this may suggest that gray and white matter alterations relate to different underlying mechanisms. Further work is needed to understand the relationship between gray and white matter alterations in childhood-onset SLE, whether the underlying mechanisms relate to immunologic, vascular, or other causes, and whether the changes are reversible or preventable. Likewise, the protective properties of intravenous steroids in maintaining white matter volumes require confirmation in larger cohorts.

Functional neuronal network activity differs with cognitive dysfunction in childhood-onset systemic lupus erythematosus

Introduction

Neuropsychiatric manifestations are common in childhood-onset systemic lupus erythematosus (cSLE) and often include neurocognitive dysfunction (NCD). Functional magnetic resonance imaging (fMRI) can measure brain activation during tasks that invoke domains of cognitive function impaired by cSLE. This study investigates specific changes in brain function attributable to NCD in cSLE that have potential to serve as imaging biomarkers.

Methods

Formal neuropsychological testing was done to measure cognitive ability and to identify NCD. Participants performed fMRI tasks probing three cognitive domains impacted by cSLE: visuoconstructional ability (VCA), working memory, and attention. Imaging data, collected on 3-Tesla scanners, included a high-resolution T1-weighted anatomic reference image followed by a T2*-weighted whole-brain echo planar image series for each fMRI task. Brain activation using blood oxygenation level-dependent contrast was compared between cSLE patients with NCD (NCD-group, n = 7) vs. without NCD (noNCD-group, n = 14) using voxel-wise and region of interest-based analyses. The relationship of brain activation during fMRI tasks and performance in formal neuropsychological testing was assessed.

Results

Greater brain activation was observed in the noNCD-group vs. NCD-group during VCA and working memory fMRI tasks. Conversely, compared to the noNCD-group, the NCD-group showed more brain activation during the attention fMRI task. In region of interest analysis, brain activity during VCA and working memory fMRI tasks was positively associated with the participants' neuropsychological test performance. In contrast, brain activation during the attention fMRI task was negatively correlated with neuropsychological test performance. While the NCD group performed worse than the noNCD group during VCA and working memory tasks, the attention task was performed equally well by both groups.

Conclusions

NCD in patients with cSLE is characterized by differential activation of functional neuronal networks during fMRI tasks probing working memory, VCA, and attention. Results suggest a compensatory mechanism allows maintenance of attentional performance under NCD. This mechanism appears to break down for the VCA and working memory challenges presented in this study. The observation that neuronal network activation is related to the formal neuropsychological testing performance makes fMRI a candidate imaging biomarker for cSLE-associated NCD.

An fMRI Study of the Interactions Between the Attention and the Gustatory Networks

In a prior study, we showed that trying to detect a taste in a tasteless solution results in enhanced activity in the gustatory and attention networks. The aim of the current study was to use connectivity analyses to test if and how these networks interact during directed attention to taste. We predicted that the attention network modulates taste cortex, reflecting top-down enhancement of incoming sensory signals that are relevant to goal-directed behavior. fMRI was used to measure brain responses in 14 subjects as they performed two different tasks: (1) trying to detect a taste in a solution or (2) passively perceiving the same solution. We used psychophysiological interaction analysis to identify regions demonstrating increased connectivity during a taste attention task compared to passive tasting. We observed greater connectivity between the anterior cingulate cortex and the frontal eye fields, posterior parietal cortex, and parietal operculum and between the anterior cingulate cortex and the right anterior insula and frontal operculum. These results suggested that selective attention to taste is mediated by a hierarchical circuit in which signals are first sent from the frontal eye fields, posterior parietal cortex, and parietal operculum to the anterior cingulate cortex, which in turn modulates responses in the anterior insula and frontal operculum. We then tested this prediction using dynamic causal modeling. This analysis confirmed a model of indirect modulation of the gustatory cortex, with the strongest influence coming from the frontal eye fields via the anterior cingulate cortex. In summary, the results indicate that the attention network modulates the gustatory cortex during attention to taste and that the anterior cingulate cortex acts as an intermediary processing hub between the attention network and the gustatory cortex.

The anterior insular cortex represents breaches of taste identity expectation

Despite the importance of breaches of taste identity expectation for survival, its neural correlate is unknown. We used fMRI in 16 women to examine brain response to expected and unexpected receipt of sweet taste and tasteless/odorless solutions. During expected trials (70%), subjects heard "sweet" or "tasteless" and received the liquid indicated by the cue. During unexpected trials (30%), subjects heard sweet but received tasteless or they heard tasteless but received sweet. After delivery, subjects indicated stimulus identity by pressing a button. Reaction time was faster and more accurate after valid cuing, indicating that the cues altered expectancy as intended. Tasting unexpected versus expected stimuli resulted in greater deactivation in fusiform gyri, possibly reflecting greater suppression of visual object regions when orienting to, and identifying, an unexpected taste. Significantly greater activation to unexpected versus expected stimuli occurred in areas related to taste (thalamus, anterior insula), reward [ventral striatum (VS), orbitofrontal cortex], and attention [anterior cingulate cortex, inferior frontal gyrus, intraparietal sulcus (IPS)]. We also observed an interaction between stimulus and expectation in the anterior insula (primary taste cortex). Here response was greater for unexpected versus expected sweet compared with unexpected versus expected tasteless, indicating that this region is preferentially sensitive to breaches of taste expectation. Connectivity analyses confirmed that expectation enhanced network interactions, with IPS and VS influencing insular responses. We conclude that unexpected oral stimulation results in suppression of visual cortex and upregulation of sensory, attention, and reward regions to support orientation, identification, and learning about salient stimuli.

The insular taste cortex contributes to odor quality coding

Despite distinct peripheral and central pathways, stimulation of both the olfactory and the gustatory systems may give rise to the sensation of sweetness. Whether there is a common central mechanism producing sweet quality sensations or two discrete mechanisms associated independently with gustatory and olfactory stimuli is currently unknown. Here we used fMRI to determine whether odor sweetness is represented in the piriform olfactory cortex, which is thought to code odor quality, or in the insular taste cortex, which is thought to code taste quality. Fifteen participants sampled two concentrations of a pure sweet taste (sucrose), two sweet food odors (chocolate and strawberry), and two sweet floral odors (lilac and rose). Replicating prior work we found that olfactory stimulation activated the piriform, orbitofrontal and insular cortices. Of these regions, only the insula also responded to sweet taste. More importantly, the magnitude of the response to the food odors, but not to the non-food odors, in this region of insula was positively correlated with odor sweetness rating. These findings demonstrate that insular taste cortex contributes to odor quality coding by representing the taste-like aspects of food odors. Since the effect was specific to the food odors, and only food odors are experienced with taste, we suggest this common central mechanism develops as a function of experiencing flavors.

Neural correlates of evaluative compared with passive tasting

We used functional magnetic resonance imaging to test the hypothesis that the nature of the neural response to taste varies as a function of the task the subject is asked to perform. Subjects received sweet, sour, salty and tasteless solutions passively and while evaluating stimulus presence, pleasantness and identity. Within the insula and overlying operculum the location of maximal response to taste vs. tasteless varied as a function of task; however, the primary taste cortex (anterior dorsal insula/frontal operculum--AIFO), as well as a more ventral region of anterior insula, responded to taste vs. tasteless irrespective of task. Although the response here did not depend upon task, preferential connectivity between AIFO and the amygdala (bilaterally) was observed when subjects tasted passively compared with when they performed a task. This suggests that information transfer between AIFO and the amygdala is maximal during implicit processing of taste. In contrast, a region of the left lateral orbitofrontal cortex (OFC) responded preferentially to taste and to tasteless when subjects evaluated pleasantness, and was preferentially connected to earlier gustatory relays (caudomedial OFC and AIFO) when a taste was present. This suggests that processing in the lateral OFC organizes the retrieval of gustatory information from earlier relays in the service of computing perceived pleasantness. These findings show that neural encoding of taste varies as a function of task beyond that of the initial cortical representation.

Sleep deprivation alters functioning within the neural network underlying the covert orienting of attention

One function of spatial attention is to enable goal-directed interactions with the environment through the allocation of neural resources to motivationally relevant parts of space. Studies have shown that responses are enhanced when spatial attention is predictively biased towards locations where significant events are expected to occur. Previous studies suggest that the ability to bias attention predictively is related to posterior cingulate cortex (PCC) activation [Small, D.M., et al., 2003. The posterior cingulate and medial prefrontal cortex mediate the anticipatory allocation of spatial attention. Neuroimage 18, 633-41]. Sleep deprivation (SD) impairs selective attention and reduces PCC activity [Thomas, M., et al., 2000. Neural basis of alertness and cognitive performance impairments during sleepiness. I. Effects of 24 h of sleep deprivation on waking human regional brain activity. J. Sleep Res. 9, 335-352]. Based on these findings, we hypothesized that SD would affect PCC function and alter the ability to predictively allocate spatial attention. Seven healthy, young adults underwent functional magnetic resonance imaging (fMRI) following normal rest and 34-36 h of SD while performing a task in which attention was shifted in response to peripheral targets preceded by spatially informative (valid), misleading (invalid), or uninformative (neutral) cues. When rested, but not when sleep-deprived, subjects responded more quickly to targets that followed valid cues than those after neutral or invalid cues. Brain activity during validly cued trials with a reaction time benefit was compared to activity in trials with no benefit. PCC activation was greater during trials with a reaction time benefit following normal rest. In contrast, following SD, reaction time benefits were associated with activation in the left intraparietal sulcus, a region associated with receptivity to stimuli at unexpected locations. These changes may render sleep-deprived individuals less able to anticipate the locations of upcoming events, and more susceptible to distraction by stimuli at irrelevant locations.

The spatial attention network interacts with limbic and monoaminergic systems to modulate motivation-induced attention shifts

How does the human brain integrate information from multiple domains to guide spatial attention according to motivational needs? To address this question, we measured hemodynamic responses to central cues predicting locations of peripheral attentional targets (food or tool images) in a novel covert spatial attention paradigm. The motivational relevance of food-related attentional targets was experimentally manipulated via hunger and satiety. Amygdala, posterior cingulate, locus coeruleus, and substantia nigra showed selective sensitivity to food-related cues when hungry but not when satiated, an effect that did not generalize to tools. Posterior parietal cortex (PPC), including intraparietal sulcus, posterior cingulate, and the orbitofrontal cortex displayed correlations with the speed of attentional shifts that were sensitive not just to motivational state but also to the motivational value of the target. Stronger functional coupling between PPC and posterior cingulate occurred during attentional biasing toward motivationally relevant food targets. These results reveal conjoint limbic and monoaminergic encoding of motivational salience in spatial attention. They emphasize the interactive role of posterior parietal and cingulate cortices in integrating motivational information with spatial attention, a process that is critical for selective allocation of attentional resources in an environment where target position and relevance can change rapidly.

Developmental changes in activation and effective connectivity in phonological processing

The current study examined developmental changes in activation and effective connectivity among brain regions during a phonological processing task, using fMRI. Participants, ages 9-15, were scanned while performing rhyming judgments on pairs of visually presented words. The orthographic and phonological similarity between words in the pair was independently manipulated, so that rhyming judgment could not be based on orthographic similarity. Our results show a developmental increase in activation in the dorsal part of left inferior frontal gyrus (IFG), accompanied by a decrease in the dorsal part of left superior temporal gyrus (STG). The coupling of dorsal IFG with other selected brain regions involved in the phonological decision increased with age, while the coupling of STG decreased with age. These results suggest that during development there is a shift from reliance on sensory auditory representations to reliance on phonological segmentation and covert articulation for performing rhyming judgment on visually presented words. In addition, we found a developmental increase in activation in left posterior parietal cortex that was not accompanied by a change in its connectivity with the other regions. These results suggest that maturational changes within a cortical region are not necessarily accompanied by an increase in its interactions with other regions and its contribution to the task. Our results are consistent with the idea that there is reduced reliance on primary sensory processes as task-relevant processes mature and become more efficient during development.

Neural correlates of verb argument structure processing

Neuroimaging and lesion studies suggest that processing of word classes, such as verbs and nouns, is associated with distinct neural mechanisms. Such studies also suggest that subcategories within these broad word class categories are differentially processed in the brain. Within the class of verbs, argument structure provides one linguistic dimension that distinguishes among verb exemplars, with some requiring more complex argument structure entries than others. This study examined the neural instantiation of verbs by argument structure complexity: one-, two-, and three-argument verbs. Stimuli of each type, along with nouns and pseudowords, were presented for lexical decision using an event-related functional magnetic resonance imaging design. Results for 14 young normal participants indicated largely overlapping activation maps for verbs and nouns, with no areas of significant activation for verbs compared to nouns, or vice versa. Pseudowords also engaged neural tissue overlapping with that for both word classes, with more widespread activation noted in visual, motor, and peri-sylvian regions. Examination of verbs by argument structure revealed activation of the supramarginal and angular gyri, limited to the left hemisphere only when verbs with two obligatory arguments were compared to verbs with a single argument. However, bilateral activation was noted when both two- and three-argument verbs were compared to one-argument verbs. These findings suggest that posterior peri-sylvian regions are engaged for processing argument structure information associated with verbs, with increasing neural tissue in the inferior parietal region associated with increasing argument structure complexity. These findings are consistent with processing accounts, which suggest that these regions are crucial for semantic integration.

Neural correlates of sexual arousal in homosexual and heterosexual men

Men exhibit much higher levels of genital and subjective arousal to sexual stimuli containing their preferred sex than they do to stimuli containing only the nonpreferred sex. This study used event-related functional magnetic resonance imaging to investigate how this category-specific pattern would be reflected in the brains of homosexual (n = 11) and heterosexual (n = 11) men. Comparisons of activation to preferred sexual stimuli, nonpreferred sexual stimuli, and sports stimuli revealed large networks correlated with sexual arousal, spanning multiple cortical and subcortical areas. Both homosexual and heterosexual men exhibited category-specific arousal in brain activity. Within the amygdala, greater preference-related activity was observed in homosexual men, but it is unclear whether this is a cause or a consequence of their sexuality. In a subsequent analysis of regions hypothesized to support arousal, both participant groups demonstrated widespread increases in evoked activity for preferred stimuli. Aggregate data from these regions produced significant differences between stimulus types in 16 out of 22 participants. Significant activational differences matched reported sexual orientation in 15 of these 16 participants, representing an advance in psychophysiological measures of arousal.

Altered effective connectivity within the language network in primary progressive aphasia

Primary progressive aphasia (PPA) is a neurodegenerative dementia syndrome principally characterized by the gradual dissolution of language functions, especially in the early stages of disorder. In a previous functional neuroimaging study, PPA patients were found to activate core language areas similarly to control subjects when performing semantic and phonological processing tasks (Sonty et al., 2003). In the present study, functional magnetic resonance imaging (fMRI) and dynamic causal modeling (DCM) were used to study multiregional effective connectivity in early-stage PPA (n = 8) and control (n = 8) subjects performing semantic word matching and visual letter matching tasks. fMRI analysis showed semantic task-specific activations in the left inferior frontal (Broca's area) and posterior superior temporal (Wernicke's area) regions, in addition to other language regions, in both groups. Using a model language network consisting of six left hemisphere regions, the DCM analysis demonstrated reduced language-specific effective connectivity between Wernicke's and Broca's areas in the PPA patient group. Furthermore, this decrement in connectivity was predictive of semantic task accuracy. These results demonstrate for the first time that dysfunctional network interactions (effective connectivity), rather than hypoactivity within individual brain regions, may contribute to the emergence of language deficits seen in PPA.

Vasectomy in Men With Primary Progressive Aphasia

OBJECTIVE

To study the frequency of vasectomy in men with primary progressive aphasia (PPA).

BACKGROUND

PPA is a dementia syndrome in which aphasia emerges in relative isolation during the initial stages of illness. On the basis of a clinical observation in a patient who dated the onset of symptoms to the period after a vasectomy, and because of the curious sharing of the tau protein exclusively by brain and sperm, vasectomy rates were examined in men with PPA.

METHOD

This study used a case control design. Forty-seven men with PPA and 57 men with no cognitive impairment (NC) between 55 and 80 years of age were surveyed about a history of vasectomy.

RESULTS

The age-adjusted rate of vasectomy in PPA patients (40%) was higher than in NC (16%, P=0.02). There was a younger age at onset for the patients with vasectomy (58.8 vs. 62.9 y, P=0.03).

CONCLUSIONS

Vasectomy may constitute one risk factor for PPA in men. Potential mechanisms mediating risk include vasectomy-induced immune responses to sperm, which shares antigenic epitopes with brain. Antisperm antibodies can also develop in women and become risk factors for PPA.

Weaker top-down modulation from the left inferior frontal gyrus in children

Previous studies have shown that developmental changes in the structure and function of prefrontal regions can continue throughout childhood and adolescence. Our recent results suggested a role for the left inferior frontal cortex in modulating task-dependent shifts in effective connectivity when adults focus on orthographic versus phonological aspects of presented words. Specifically, the top-down influence of the inferior frontal cortex determined whether incoming word-form information from the fusiform gyrus would have a greater impact on the parietal areas involved in orthographic processing or temporal areas involved in phonological processing (Bitan, T., Booth, J.R., Choy, J., Burman, D.D., Gitelman, D.R. and Mesulam, M.-M., 2005. Shifts of Effective Connectivity within a Language Network during Rhyming and Spelling. J. Neurosci. 25, 5397-5403.). In the current study, we find that children displayed an identical pattern of task-dependent functional activations within this network. In comparison to adults, however, children had significantly weaker top-down modulatory influences emanating from the inferior frontal area. Adult language processing may thus involve greater top-down cognitive control compared to children, resulting in less interference from task-irrelevant information.

Taste and olfactory intensity perception changes following left insular stroke

The authors tested suprathreshold intensity perception of gustatory and olfactory stimuli in a 70-year-old right-handed man following a left posterior insular stroke and compared his results with those of age-matched controls. Both modalities revealed significant differences between left (ipsilateral to lesion) and right (contralateral) ratings of intensity. In both gustation and olfaction, these differences were driven primarily by trends toward increased contralateral sensitivity relative to controls. Intensity changes were most pronounced for unpleasant odors and for tastes perceived strongly as either pleasant (sweet) or unpleasant (salty, bitter). These results show that a left posterior insula lesion may affect taste and olfactory perception similarly by increasing sensitivity contralateral to the lesion. One possible mechanism is release from inhibition at the cortical level.

Orienting Attention Based on Long-Term Memory Experience

Attentional orienting and memory are intrinsically bound, but their interaction has rarely been investigated. Here we introduce an experimental paradigm using naturalistic scenes to investigate how long-term memory can guide spatial attention and thereby enhance identification of events in the perceptual domain. In the task, stable memories of objects embedded within complex scenes guide spatial orienting. We compared the behavioral effects and neural systems of memory-guided orienting with those in a more traditional attention-orienting task in which transient spatial cues guide attention. Memory-guided attention operated within surprisingly short intervals and conferred reliable and sizeable advantages for detection of objects embedded in scenes. Event-related functional magnetic resonance imaging showed that memory-guided attention involves the interaction between brain areas participating in retrieval of memories for spatial context with the parietal-frontal network for visual spatial orienting. Activity in the hippocampus was specifically engaged in memory-guided spatial attention and correlated with the ensuing behavioral advantage.

Neural correlates of rule-based and information-integration visual category learning

An emerging theory of the neurobiology of category learning postulates that there are separate neural systems supporting the learning of categories based on verbalizeable rules (RB) or through implicit information integration (II). The medial temporal lobe (MTL) is thought to play a crucial role in successful RB categorization, whereas the posterior regions of the caudate are hypothesized to support II categorization. Functional neuroimaging was used to assess activity in these systems during category-learning tasks with category structures designed to afford either RB or II learning. Successful RB categorization was associated with relatively increased activity in the anterior MTL. Successful II categorization was associated with increased activity in the caudate body. The dissociation observed with neuroimaging is consistent with the roles of these systems in memory and dissociations reported in patient populations. Convergent evidence from these approaches consistently reinforces the idea of multiple neural systems supporting category learning.

The "zoom lens" of focal attention in visual search: changes in aging and Alzheimer's disease

Visual search for a target in an array of distractors relies upon flexible shifts between global and local modes of attentional processing. Visual search is slowed in patients with Alzheimer's disease (AD), in part due to an increase in the number and duration of eye fixations made en route to a target (Rösler et al., 2000). This phenomenon may represent a compensatory adaptation to a narrowing of the zone of focal attention, necessitating more shifts of gaze in order to attend to the global workspace. Eye fixations were analyzed in two regions of interest (ROIs, central fixation and peripheral target locations) in 9 patients with mild AD, 9 cognitively intact age-matched control subjects, and 9 young controls, while they searched for a target object in a radial array that contained from 1 to 6 stimuli. Contrasted with young subjects, the search strategy of older controls and, to a greater extent, AD patients showed an increase in the average number and duration of peripheral fixations. Reduced efficiency of visual search in AD may be contributed to by reduced ability to dynamically adjust the attentional zoom, coupled with the inability to disengage attention from peripheral targets.

Simultaneous assessment of motor and language areas with a single functional MR imaging paradigm: feasibility

The purpose of this study was to test a hybrid multitask paradigm in healthy subjects and in a patient at preoperative functional magnetic resonance (MR) imaging. In this new paradigm, tasks related to different centers of brain function (motor and language) are performed in alternation during a single functional MR imaging examination, without the typical rest period, to improve time efficiency without compromising the quality of activation maps. The institutional review board approved the study, and all participants gave informed prior consent. The study complied with the Health Insurance Portability and Accountability Act. Seven healthy right-handed volunteers (four men, three women; age range, 22-40 years) were studied first. In both individual and group analyses, there was no statistically significant difference in results between assessment with the multitask design and that with the traditional block design. An advantage of the new paradigm was substantial time savings because the subject was engaged during the entire examination. Finally, the multitask design was tested in a patient undergoing preoperative evaluation, with similar results; therefore, use of the multitask design is feasible in a clinical setting.

Language network specializations: an analysis with parallel task designs and functional magnetic resonance imaging

Although the classical core regions of the language system (Broca's and Wernicke's areas) were defined over a century ago, it took the advent of functional imaging to sharpen our understanding of how these regions and adjacent parts of the brain are associated with particular aspects of language. One limitation of such studies has been the need to compare results across different subject groups, each performing a different type of language task. Thus, this study was designed to examine overlapping versus segregated brain activations associated with three fundamental language tasks, orthography, phonology and semantics performed by the same subjects during a single experimental session. The results demonstrate a set of primarily left-sided core language regions in ventrolateral frontal, supplementary motor, posterior mid-temporal, occipito-temporal and inferior parietal areas, which were activated for all language tasks. Segregated task-specific activations were demonstrated within the ventrolateral frontal, mid-temporal and inferior parietal areas. Within the inferior frontal cortex (Broca's regional complex), segregated activations were seen for the semantic and phonological tasks. These findings demonstrate both common and task specific activations within the language system.

Chronic back pain is associated with decreased prefrontal and thalamic gray matter density

The role of the brain in chronic pain conditions remains speculative. We compared brain morphology of 26 chronic back pain (CBP) patients to matched control subjects, using magnetic resonance imaging brain scan data and automated analysis techniques. CBP patients were divided into neuropathic, exhibiting pain because of sciatic nerve damage, and non-neuropathic groups. Pain-related characteristics were correlated to morphometric measures. Neocortical gray matter volume was compared after skull normalization. Patients with CBP showed 5-11% less neocortical gray matter volume than control subjects. The magnitude of this decrease is equivalent to the gray matter volume lost in 10-20 years of normal aging. The decreased volume was related to pain duration, indicating a 1.3 cm3 loss of gray matter for every year of chronic pain. Regional gray matter density in 17 CBP patients was compared with matched controls using voxel-based morphometry and nonparametric statistics. Gray matter density was reduced in bilateral dorsolateral prefrontal cortex and right thalamus and was strongly related to pain characteristics in a pattern distinct for neuropathic and non-neuropathic CBP. Our results imply that CBP is accompanied by brain atrophy and suggest that the pathophysiology of chronic pain includes thalamocortical processes.

Shifts of effective connectivity within a language network during rhyming and spelling

We used functional magnetic resonance imaging to examine task-specific modulations of effective connectivity within a left-hemisphere language network during spelling and rhyming judgments on visually presented words. We identified sites showing task-specific activations for rhyming in the lateral temporal cortex (LTC) and for spelling in the intraparietal sulcus (IPS). The inferior frontal gyrus (IFG) and fusiform gyrus were engaged by both tasks. Dynamic causal modeling showed that each task preferentially strengthened modulatory influences converging on its task-specific site (LTC for rhyming, IPS for spelling). These remarkably selective and symmetrical findings demonstrate that the nature of the behavioral task dynamically shifts the locus of integration (or convergence) to the network component specialized for that task. Furthermore, they suggest that the role of the task-selective areas is to provide a differential synthesis of incoming information rather than providing differential control signals influencing the activity of other network components. Our findings also showed that switching tasks led to changes in the target area influenced by the IFG, suggesting that the IFG may play a pivotal role in setting the cognitive context for each task. We propose that task-dependent shifts in effective connectivity are likely to be mediated through top-down modulations from the IFG to the task-selective regions in a way that differentially enhances their sensitivity to incoming word-form information.

Larger deficits in brain networks for response inhibition than for visual selective attention in attention deficit hyperactivity disorder (ADHD)

BACKGROUND

Brain activation differences between 12 control and 12 attention deficit hyperactivity disorder (ADHD) children (9- to 12-year-olds) were examined on two cognitive tasks during functional magnetic resonance imaging (fMRI).

METHOD

Visual selective attention was measured with the visual search of a conjunction target (red triangle) in a field of distracters and response inhibition was measured with a go/no-go task.

RESULTS

There were limited group differences in the selective attention task, with control children showing significantly greater intensity of activation in a small area of the superior parietal lobule region of interest. There were large group differences in the response inhibition task, with control children showing significantly greater intensity of activation in fronto-striatal regions of interest including the inferior, middle, superior and medial frontal gyri as well as the caudate nucleus and globus pallidus.

CONCLUSION

The widespread hypoactivity for the ADHD children on the go/no-go task is consistent with the hypothesis that response inhibition is a specific deficit in attention deficit hyperactivity disorder.

Brain-behavior correlation in children depends on the neurocognitive network

We examined brain-behavior correlations in 12 children (age range 9.3 to 11.7 years) during a selective attention task that required the visual search of a conjunction of features and during a response inhibition task that required the inhibition of a pre-potent response during "no-go" blocks. We found that the association between performance in these tasks and brain activation as measured by functional magnetic resonance imaging (fMRI) depended on the neurocognitive network. Specifically, better performance during the no-go task was associated with greater activation in the response inhibition network including the prefrontal cortex and basal ganglia. In contrast, better performance during the visual search task was associated with less activation in the selective attention network including superior parietal lobule and lateral premotor cortex. These results show that the relation of performance to the magnitude of neural activation is complex and may display differential relationships based on the cognitive domain, anatomical region, and perhaps also developmental stage.

Development of brain mechanisms for processing orthographic and phonologic representations

Developmental differences in the neurocognitive networks for lexical processing were examined in 15 adults and 15 children (9- to 12-year-olds) using functional magnetic resonance imaging (fMRI). The lexical tasks involved spelling and rhyming judgments in either the visual or auditory modality. These lexical tasks were compared with nonlinguistic control tasks involving judgments of line patterns or tone sequences. The first main finding was that adults showed greater activation than children during the cross-modal lexical tasks in a region proposed to be involved in mapping between orthographic and phonologic representations. The visual rhyming task, which required conversion from orthography to phonology, produced greater activation for adults in the angular gyrus. The auditory spelling task, which required the conversion from phonology to orthography, also produced greater activation for adults in the angular gyrus. The greater activation for adults suggests they may have a more elaborated posterior heteromodal system for mapping between representational systems. The second main finding was that adults showed greater activation than children during the intra-modal lexical tasks in the angular gyrus. The visual spelling and auditory rhyming did not require conversion between orthography and phonology for correct performance but the adults showed greater activation in a system implicated for this mapping. The greater activation for adults suggests that they have more interactive convergence between representational systems during lexical processing.

Neural Evidence That Vivid Imagining Can Lead to False Remembering

The imperfect nature of memory is highlighted by the regularity with which people fail to remember, or worse, remember something that never happened. We investigated the formation of a particular type of erroneous memory by monitoring brain activity using functional magnetic resonance imaging during the presentation of words and photos. Participants generated a visual image of a common object in response to each word. Subsequently, they sometimes claimed to have seen photos of specific objects they had imagined but not actually seen. In precuneus and inferior parietal regions of the cerebral cortex, activations in response to words were greater when participants subsequently claimed to have seen the corresponding object than when a false memory for that object was not subsequently produced. These findings indicate that brain activity reflecting the engagement of visual imagery can lead to falsely remembering something that was only imagined.

Priming Effects in the Fusiform Gyrus: Changes in Neural Activity beyond the Second Presentation

Repetition priming typically leads to a decrease in the activation of sensory cortical areas upon a second exposure to the same visual stimulus. This effect is thought to reflect more efficient or fluent re-processing of previously seen stimuli so that less neural activity is required. Fluent re-processing has been hypothesized to be a potential link from repetition priming to neural changes associated with visual expertise. To examine this potential connection, the neural correlates of priming were examined across eight stimulus repetitions using functional magnetic resonance imaging. Sizeable regions of bilateral ventral occipito-temporal cortex (including the fusiform gyrus) exhibited reduced responses to the second presentation of a stimulus. Most of these areas displayed no further reduction in response to subsequent repetitions of the same stimuli. Because expertise accrues over many exposures, these areas, while clearly involved in priming, do not exhibit an activity pattern consistent with the development of expertise. In contrast, an area in the right posterior fusiform gyrus exhibited reductions in evoked response that grew in magnitude for stimulus repetitions from the second to the eighth presentations. This region exhibits a pattern of activity consistent with a gradual and cumulative enhancement of the fluency effect across trials, suggesting that it may mediate the link between priming and the development of visual expertise.

Neural development of selective attention and response inhibition

Brain activation differences between 12 children (9- to 12-year-olds) and 12 adults (20- to 30-year-olds) were examined on two cognitive tasks during functional magnetic resonance imaging (fMRI). Spatial selective attention was measured with the visual search for a conjunction target (red triangle) in a field of distracters and response inhibition was measured with a go no-go task. There were small developmental differences in the selective attention task, with children showing greater activation than adults in the anterior cingulate and thalamus. There were large developmental differences in the response inhibition task, with children showing greater activation than adults in a fronto-striatal network including middle cingulate, medial frontal gyrus, medial aspects of bilateral superior frontal gyrus, and the caudate nucleus on the left. Children also showed greater bilateral activation for the response inhibition task in posterior cingulate, thalamus and the hippocampo-amygdaloid region. The extensive developmental differences on the response inhibition task are consistent with the prolonged maturation of the fronto-striatal network.

Cerebral hemispheric specialization for spatial attention: spatial distribution of search-related eye fixations in the absence of neglect

The "specialization" of the right hemisphere for spatial attention is widely accepted but poorly understood. While several theories have been supported by studies of patients with acute hemispatial neglect, generalizability beyond this population remains unclear. In this study, we compared the predictions of two attention models [Brain 119 (1996) 841; Trans. Am. Neurol. Assoc. 95 (1970) 143] when applied to data obtained from subjects with unilateral right- or left-cerebral lesions, but without clinical evidence of neglect during a visual search task. Both Left Lesion and Right Lesion subjects detected fewer targets in the contralesional hemispace. However, the Right Lesion subjects also made fewer visual fixations and longer saccades in the contralesional hemispace, suggesting a fundamental alteration in the architecture of visual search. The spatial distribution of fixations made by Right Lesion subjects more closely fits the prediction of a "salience" model than of the strict interpretation of a linear "gradient" model. These data support the long-standing notion of right hemisphere dominance for spatial attention, especially for the top-down processes entailed in self-directed visual search, and extend this to lesion patients without clinically evident neglect. A theoretical model based on the salience of extrapersonal space appears useful for understanding alterations of attentional allocation, particularly after recovery from stroke.

Brain networks for analyzing eye gaze

The eyes convey a wealth of information in social interactions. This information is analyzed by multiple brain networks, which we identified using functional magnetic resonance imaging (MRI). Subjects attempted to detect a particular directional cue provided either by gaze changes on an image of a face or by an arrow presented alone or by an arrow superimposed on the face. Another control condition was included in which the eyes moved without providing meaningful directional information. Activation of the superior temporal sulcus accompanied extracting directional information from gaze relative to directional information from an arrow and relative to eye motion without relevant directional information. Such selectivity for gaze processing was not observed in face-responsive fusiform regions. Brain activations were also investigated while subjects viewed the same face but attempted to detect when the eyes gazed directly at them. Most notably, amygdala activation was greater during periods when direct gaze never occurred than during periods when direct gaze occurred on 40% of the trials. In summary, our results suggest that increases in neural processing in the amygdala facilitate the analysis of gaze cues when a person is actively monitoring for emotional gaze events, whereas increases in neural processing in the superior temporal sulcus support the analysis of gaze cues that provide socially meaningful spatial information.

Neural correlates of person recognition

Rapidly identifying known individuals is an essential skill in human society. To elucidate the neural basis of this skill, we monitored brain activity while experimental participants demonstrated their ability to recognize people on the basis of viewing their faces. Each participant first memorized the faces of 20 individuals who were not known to the participants in advance. Each face was presented along with a voice simulating the individual speaking their name and a biographical fact. Following this learning procedure, the associated verbal information could be recalled accurately in response to each face. These learned faces were subsequently viewed together with new faces in a memory task. Subjects made a yes-no recognition decision in response to each face while also covertly retrieving the person-specific information associated with each learned face. Brain activity that accompanied this retrieval of person-specific information was contrasted to that when new faces were processed. Functional magnetic resonance imaging in 10 participants showed that several brain regions were activated during blocks of learned faces, including left hippocampus, left middle temporal gyrus, left insula, and bilateral cerebellum. Recordings of event-related brain potentials in 10 other participants tracked the time course of face processing and showed that learned faces engaged neural activity responsible for person recognition 300-600 msec after face onset. Collectively, these results suggest that the visual input of a recently learned face can rapidly trigger retrieval of associated person-specific information through reactivation of distributed cortical networks linked via hippocampal connections.

Dissociating explicit and implicit category knowledge with fMRI

Neuroimaging of healthy volunteers identified separate neural systems supporting the expression of category knowledge depending on whether the learning mode was intentional or incidental. The same visual category was learned either intentionally or implicitly by two separate groupsof participants. During a categorization test, functional magnetic resonance imaging (fMRI) was used to compare brain activity evoked by category members and nonmembers. After implicit learning, when participants had learned the category incidentally, decreased occipital activity was observed for novel categorical stimuli compared with noncategorical stimuli. In contrast, after intentional learning, novel categorical stimuli evoked increased activity in the hippocampus, right prefrontal cortex, left inferior temporal cortex, precuneus, and posterior cingulate. Even though the categorization test was identical in the two conditions, the differences in brain activity indicate differing representations of category knowledge depending on whether the category had been learned intentionally or implicitly.

Modeling regional and psychophysiologic interactions in fMRI: the importance of hemodynamic deconvolution

The analysis of functional magnetic resonance imaging (fMRI) time-series data can provide information not only about task-related activity, but also about the connectivity (functional or effective) among regions and the influences of behavioral or physiologic states on that connectivity. Similar analyses have been performed in other imaging modalities, such as positron emission tomography. However, fMRI is unique because the information about the underlying neuronal activity is filtered or convolved with a hemodynamic response function. Previous studies of regional connectivity in fMRI have overlooked this convolution and have assumed that the observed hemodynamic response approximates the neuronal response. In this article, this assumption is revisited using estimates of underlying neuronal activity. These estimates use a parametric empirical Bayes formulation for hemodynamic deconvolution.

Relation between brain activation and lexical performance

Functional magnetic resonance imaging (fMRI) was used to determine whether performance on lexical tasks was correlated with cerebral activation patterns. We found that such relationships did exist and that their anatomical distribution reflected the neurocognitive processing routes required by the task. Better performance on intramodal tasks (determining if visual words were spelled the same or if auditory words rhymed) was correlated with more activation in unimodal regions corresponding to the modality of sensory input, namely the fusiform gyrus (BA 37) for written words and the superior temporal gyrus (BA 22) for spoken words. Better performance in tasks requiring cross-modal conversions (determining if auditory words were spelled the same or if visual words rhymed), on the other hand, was correlated with more activation in posterior heteromodal regions, including the supramarginal gyrus (BA 40) and the angular gyrus (BA 39). Better performance in these cross-modal tasks was also correlated with greater activation in unimodal regions corresponding to the target modality of the conversion process (i.e., fusiform gyrus for auditory spelling and superior temporal gyrus for visual rhyming). In contrast, performance on the auditory spelling task was inversely correlated with activation in the superior temporal gyrus possibly reflecting a greater emphasis on the properties of the perceptual input rather than on the relevant transmodal conversions.

The posterior cingulate and medial prefrontal cortex mediate the anticipatory allocation of spatial attention

The purpose of this study was to identify brain regions underlying internally generated anticipatory biases toward locations where significant events are expected to occur. Subjects fixated centrally and responded to peripheral targets preceded by a spatially valid (predictive), invalid (misleading), or neutral central cue while undergoing fMRI scanning. In some validly cued trials, reaction time was significantly shorter than in trials with neutral cues, indicating that the cue had successfully induced a spatial redistribution of motivational valence, manifested as expectancy. The largest cue benefits led to selectively greater activations within the posterior cingulate and medial prefrontal cortex. These two areas thus appear to establish a neural interface between attention and motivation. An inverse relationship to cue benefit was seen in the parietal cortex, suggesting that spatial expectancy may entail the inhibition of attention-related areas to reduce distractibility by events at irrelevant locations.

Attention and its disorders

This chapter focuses on the clinical aspects of attention including anatomy, cognitive neuropsychology, disorders, and functional imaging evidence for the role of attention in cognition. Particular emphasis is given to selected aspects of visual attention. Imaging studies discussed are primarily functional magnetic resonance imaging (fMRI) and positron emission tomography (PET). In addition, some evidence will be provided from the time-honoured clinical method of lesion studies.