Abnormal processing of visual motion in dyslexia revealed by functional brain imaging

It is widely accepted that dyslexics have deficits in reading and phonological awareness, but there is increasing evidence that they also exhibit visual processing abnormalities that may be confined to particular portions of the visual system. In primate visual pathways, inputs from parvocellular or magnocellular layers of the lateral geniculate nucleus remain partly segregated in projections to extrastriate cortical areas specialized for processing colour and form versus motion. In studies of dyslexia, psychophysical and anatomical evidence indicate an anomaly in the magnocellular visual subsystem. To investigate the pathophysiology of dyslexia, we used functional magnetic resonance imaging (fMRI) to study visual motion processing in normal and dyslexic men. In all dyslexics, presentation of moving stimuli failed to produce the same task-related functional activation in area V5/MT (part of the magnocellular visual subsystem) observed in controls. In contrast, presentation of stationary patterns resulted in equivalent activations in V1/V2 and extrastriate cortex in both groups. Although previous studies have emphasized language deficits, our data reveal differences in the regional functional organization of the cortical visual system in dyslexia.

Hierarchical organization of the human auditory cortex revealed by functional magnetic resonance imaging

The concept of hierarchical processing--that the sensory world is broken down into basic features later integrated into more complex stimulus preferences--originated from investigations of the visual cortex. Recent studies of the auditory cortex in nonhuman primates revealed a comparable architecture, in which core areas, receiving direct input from the thalamus, in turn, provide input to a surrounding belt. Here functional magnetic resonance imaging (fMRI) shows that the human auditory cortex displays a similar hierarchical organization: pure tones (PTs) activate primarily the core, whereas belt areas prefer complex sounds, such as narrow-band noise bursts.

Preserved functional specialization for spatial processing in the middle occipital gyrus of the early blind

The occipital cortex (OC) of early-blind humans is activated during various nonvisual perceptual and cognitive tasks, but little is known about its modular organization. Using functional MRI we tested whether processing of auditory versus tactile and spatial versus nonspatial information was dissociated in the OC of the early blind. No modality-specific OC activation was observed. However, the right middle occipital gyrus (MOG) showed a preference for spatial over nonspatial processing of both auditory and tactile stimuli. Furthermore, MOG activity was correlated with accuracy of individual sound localization performance. In sighted controls, most of extrastriate OC, including the MOG, was deactivated during auditory and tactile conditions, but the right MOG was more activated during spatial than nonspatial visual tasks. Thus, although the sensory modalities driving the neurons in the reorganized OC of blind individuals are altered, the functional specialization of extrastriate cortex is retained regardless of visual experience.

Dysmaturation of the default mode network in autism

Two hypotheses of autism spectrum disorder (ASD) propose that this condition is characterized by deficits in Theory of Mind and by hypoconnectivity between remote cortical regions with hyperconnectivity locally. The default mode network (DMN) is a set of remote, functionally connected cortical nodes less active during executive tasks than at rest and is implicated in Theory of Mind, episodic memory, and other self-reflective processes. We show that children with ASD have reduced connectivity between DMN nodes and increased local connectivity within DMN nodes and the visual and motor resting-state networks. We show that, like the trajectory of synaptogenesis, internodal DMN functional connectivity increased as a quadratic function of age in typically developing children, peaking between, 11 and 13 years. In children with ASD, these long-distance connections fail to develop during adolescence. These findings support the "developmental disconnection model" of ASD, provide a possible mechanistic explanation for the Theory-of-Mind hypothesis of ASD, and show that the window for effectively treating ASD could be wider than previously thought.

Mediation of the relationship between callous-unemotional traits and proactive aggression by amygdala response to fear among children with conduct problems

IMPORTANCE

Among youths with conduct problems, callous-unemotional (CU) traits are known to be an important determinant of symptom severity, prognosis, and treatment responsiveness. But positive correlations between conduct problems and CU traits result in suppressor effects that may mask important neurobiological distinctions among subgroups of children with conduct problems.

OBJECTIVE

To assess the unique neurobiological covariates of CU traits and externalizing behaviors in youths with conduct problems and determine whether neural dysfunction linked to CU traits mediates the link between callousness and proactive aggression.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional case-control study involved behavioral testing and neuroimaging that were conducted at a university research institution. Neuroimaging was conducted using a 3-T Siemens magnetic resonance imaging scanner. It included 46 community-recruited male and female juveniles aged 10 to 17 years, including 16 healthy control participants and 30 youths with conduct problems with both low and high levels of CU traits.

MAIN OUTCOMES AND MEASURES

Blood oxygenation level-dependent signal as measured via functional magnetic resonance imaging during an implicit face-emotion processing task and analyzed using whole-brain and region of interest-based analysis of variance and multiple-regression analyses.

RESULTS

Analysis of variance revealed no group differences in the amygdala. By contrast, consistent with the existence of suppressor effects, multiple-regression analysis found amygdala responses to fearful expressions to be negatively associated with CU traits (x = 26, y = 0, z = -12; k = 1) and positively associated with externalizing behavior (x = 24, y = 0, z = -14; k = 8) when both variables were modeled simultaneously. Reduced amygdala responses mediated the relationship between CU traits and proactive aggression.

CONCLUSIONS AND RELEVANCE

The results linked proactive aggression in youths with CU traits to hypoactive amygdala responses to emotional distress cues, consistent with theories that externalizing behaviors, particularly proactive aggression, in youths with these traits stem from deficient empathic responses to distress. Amygdala hypoactivity may represent an intermediate phenotype, offering new insights into effective treatment strategies for conduct problems.

Cancer-Related Cognitive Outcomes Among Older Breast Cancer Survivors in the Thinking and Living With Cancer Study

PURPOSE

To determine treatment and aging-related effects on longitudinal cognitive function in older breast cancer survivors.

METHODS

Newly diagnosed nonmetastatic breast cancer survivors (n = 344) and matched controls without cancer (n = 347) 60 years of age and older without dementia or neurologic disease were recruited between August 2010 and December 2015. Data collection occurred during presystemic treatment/control enrollment and at 12 and 24 months through biospecimens; surveys; self-reported Functional Assessment of Cancer Therapy-Cognitive Function; and neuropsychological tests that measured attention, processing speed, and executive function (APE) and learning and memory (LM). Linear mixed-effects models tested two-way interactions of treatment group (control, chemotherapy with or without hormonal therapy, and hormonal therapy) and time and explored three-way interactions of ApoE (ε4+ v not) by group by time; covariates included baseline age, frailty, race, and cognitive reserve.

RESULTS

Survivors and controls were 60 to 98 years of age, were well educated, and had similar baseline cognitive scores. Treatment was related to longitudinal cognition scores, with survivors who received chemotherapy having increasingly worse APE scores ( P = .05) and those initiating hormonal therapy having lower LM scores at 12 months ( P = .03) than other groups. These group-by-time differences varied by ApoE genotype, where only ε4+ survivors receiving hormone therapy had short-term decreases in adjusted LM scores (three-way interaction P = .03). For APE, the three-way interaction was not significant ( P = .14), but scores were significantly lower for ε4+ survivors exposed to chemotherapy (-0.40; 95% CI, -0.79 to -0.01) at 24 months than ε4+ controls (0.01; 95% CI, 0.16 to 0.18; P < .05). Increasing age was associated with lower baseline scores on all cognitive measures ( P < .001); frailty was associated with baseline APE and self-reported decline ( P < .001).

CONCLUSION

Breast cancer systemic treatment and aging-related phenotypes and genotypes are associated with longitudinal decreases in cognitive function scores in older survivors. These data could inform treatment decision making and survivorship care planning.

Attention to single letters activates left extrastriate cortex

Brain imaging studies examining the component processes of reading using words, non-words, and letter strings frequently report task-related activity in the left extrastriate cortex. Processing of these linguistic materials involves varying degrees of semantic, phonological, and orthographic analysis that are sensitive to individual differences in reading skill and history. In contrast, single letter processing becomes automatized early in life and is not modulated by later linguistic experience to the same degree as are words. In this study, skilled readers attended to different aspects (single letters, symbols, and colors) of an identical stimulus set during separate sessions of functional magnetic resonance imaging (fMRI). Whereas activation in some portions of ventral extrastriate cortex was shared by attention to both alphabetic and non-alphabetic features, a letter-specific area was identified in a portion of left extrastriate cortex (Brodmann's Area 37), lateral to the visual word form area. Our results demonstrate that while minimizing activity related to word-level lexical properties, cortical responses to letter recognition can be isolated from figural and color characteristics of simple stimuli. The practical utility of this finding is discussed in terms of early identification of reading disability.

Cognitive effects of cancer and its treatments at the intersection of aging: what do we know; what do we need to know?

There is a fairly consistent, albeit non-universal body of research documenting cognitive declines after cancer and its treatments. While few of these studies have included subjects aged 65 years and older, it is logical to expect that older patients are at risk of cognitive decline. Here, we use breast cancer as an exemplar disease for inquiry into the intersection of aging and cognitive effects of cancer and its therapies. There are a striking number of common underlying potential biological risks and pathways for the development of cancer, cancer-related cognitive declines, and aging processes, including the development of a frail phenotype. Candidate shared pathways include changes in hormonal milieu, inflammation, oxidative stress, DNA damage and compromised DNA repair, genetic susceptibility, decreased brain blood flow or disruption of the blood-brain barrier, direct neurotoxicity, decreased telomere length, and cell senescence. There also are similar structure and functional changes seen in brain imaging studies of cancer patients and those seen with "normal" aging and Alzheimer's disease. Disentangling the role of these overlapping processes is difficult since they require aged animal models and large samples of older human subjects. From what we do know, frailty and its low cognitive reserve seem to be a clinically useful marker of risk for cognitive decline after cancer and its treatments. This and other results from this review suggest the value of geriatric assessments to identify older patients at the highest risk of cognitive decline. Further research is needed to understand the interactions between aging, genetic predisposition, lifestyle factors, and frailty phenotypes to best identify the subgroups of older patients at greatest risk for decline and to develop behavioral and pharmacological interventions targeting this group. We recommend that basic science and population trials be developed specifically for older hosts with intermediate endpoints of relevance to this group, including cognitive function and trajectories of frailty. Clinicians and their older patients can advance the field by active encouragement of and participation in research designed to improve the care and outcomes of the growing population of older cancer patients.

Cholinergic stimulation alters performance and task-specific regional cerebral blood flow during working memory

Modulation of the cholinergic neurotransmitter system results in changes in memory performance, including working memory (WM), in animals and in patients with Alzheimer disease. To identify associated changes in the functional brain response, we studied performance measures and regional cerebral blood flow (rCBF) using positron emission tomography (PET) in healthy subjects during performance of a WM task. Eight control subjects received an infusion of saline throughout the study and 13 experimental subjects received a saline infusion for the first 2 scans followed by a continuous infusion of physostigmine, an acetylcholinesterase inhibitor, for the subsequent 8 scans. rCBF was measured using H215O and PET in a sequence of 10 PET scans that alternated between rest and task scans. During task scans, subjects performed the WM task for faces. Physostigmine both improved WM efficiency, as indicated by faster reaction times, and reduced WM task-related activity in anterior and posterior regions of right midfrontal gyrus, a region shown previously to be associated with WM. Furthermore, the magnitudes of physostigmine-induced change in reaction time and right midfrontal rCBF correlated. These results suggest that enhancement of cholinergic function can improve processing efficiency and thus reduce the effort required to perform a WM task, and that activation of right prefrontal cortex is associated with task effort.

Neural and cognitive characteristics of extraordinary altruists

Altruistic behavior improves the welfare of another individual while reducing the altruist's welfare. Humans' tendency to engage in altruistic behaviors is unevenly distributed across the population, and individual variation in altruistic tendencies may be genetically mediated. Although neural endophenotypes of heightened or extreme antisocial behavior tendencies have been identified in, for example, studies of psychopaths, little is known about the neural mechanisms that support heightened or extreme prosocial or altruistic tendencies. In this study, we used structural and functional magnetic resonance imaging to assess a population of extraordinary altruists: altruistic kidney donors who volunteered to donate a kidney to a stranger. Such donations meet the most stringent definitions of altruism in that they represent an intentional behavior that incurs significant costs to the donor to benefit an anonymous, nonkin other. Functional imaging and behavioral tasks included face-emotion processing paradigms that reliably distinguish psychopathic individuals from controls. Here we show that extraordinary altruists can be distinguished from controls by their enhanced volume in right amygdala and enhanced responsiveness of this structure to fearful facial expressions, an effect that predicts superior perceptual sensitivity to these expressions. These results mirror the reduced amygdala volume and reduced responsiveness to fearful facial expressions observed in psychopathic individuals. Our results support the possibility of a neural basis for extraordinary altruism. We anticipate that these findings will expand the scope of research on biological mechanisms that promote altruistic behaviors to include neural mechanisms that support affective and social responsiveness.

Regional differences in the developmental trajectory of lateralization of the language network

The timing and developmental factors underlying the establishment of language dominance are poorly understood. We investigated the degree of lateralization of traditional frontotemporal and modulatory prefrontal-cerebellar regions of the distributed language network in children (n = 57) ages 4 to 12--a critical period for language consolidation. We examined the relationship between the strength of language lateralization and neuropsychological measures and task performance. The fundamental language network is established by four with ongoing maturation of language functions as evidenced by strengthening of lateralization in the traditional frontotemporal language regions; temporal regions were strongly and consistently lateralized by age seven, while frontal regions had greater variability and were less strongly lateralized through age 10. In contrast, the modulatory prefrontal-cerebellar regions were the least strongly lateralized and degree of lateralization was not associated with age. Stronger core language skills were significantly correlated with greater right lateralization in the cerebellum.

Functional connectivity of the inferior frontal cortex changes with age in children with autism spectrum disorders: a fcMRI study of response inhibition

Unmasking the neural basis of neurodevelopmental disorders, such as autism spectrum disorders (ASD), requires studying functional connectivity during childhood when cognitive skills develop. A functional connectivity magnetic resonance imaging (fcMRI) analysis was performed on data collected during Go/NoGo task performance from 24 children ages 8-12 years (12 with ASD; 12 controls matched on age and intellectual functioning). We investigated the connectivity of the left and right inferior frontal cortex (IFC; BA 47), key regions for response inhibition, with other active regions in frontal, striatal, and parietal cortex. Groups did not differ on behavioral measures or functional connectivity of either IFC region. A trend for reduced connectivity in the right IFC for the ASD group was revealed when controlling for age. In the ASD group, there was a significant negative correlation between age and 2 right IFC correlation pairs: right IFC-bilateral presupplementary motor area (BA 6) and right IFC-right caudate. Compared with typical controls, children with ASD may not have gross differences in IFC functional connectivity during response inhibition, which contrasts with an adult study of ASD that reported reduced functional connectivity. This discrepancy suggests an atypical developmental trajectory in ASD for right IFC connectivity with other neural regions supporting response inhibition.

Changes in resting state effective connectivity in the motor network following rehabilitation of upper extremity poststroke paresis

BACKGROUND

A promising paradigm in human neuroimaging is the study of slow (<0.1 Hz) spontaneous fluctuations in the hemodynamic response measured by functional magnetic resonance imaging (fMRI). Spontaneous activity (i.e., resting state) refers to activity that cannot be attributed to specific inputs or outputs, that is, activity intrinsically generated by the brain.

METHOD

This article presents pilot data examining neural connectivity in patients with poststroke hemiparesis before and after 3 weeks of upper extremity rehabilitation in the Accelerated Skill Acquisition Program (ASAP). Resting-state fMRI data acquired pre and post therapy were analyzed using an exploratory adaptation of structural equation modeling (SEM) to evaluate therapy-related changes in motor network effective connectivity.

RESULTS

Each ASAP patient showed behavioral improvement. ASAP patients also showed increased influence of the affected hemisphere premotor cortex (a-PM) upon the unaffected hemisphere premotor cortex (u-PM) following therapy. The influence of a-PM on affected hemisphere primary motor cortex (a-M1) also increased with therapy for 3 of 5 patients, including those with greatest behavioral improvement.

CONCLUSIONS

Our findings suggest that network analyses of resting-state fMRI constitute promising tools for functional characterization of functional brain disorders, for intergroup comparisons, and potentially for assessing effective connectivity within single subjects; all of which have important implications for stroke rehabilitation.

Visual cortical dysfunction in Alzheimer's disease evaluated with a temporally graded "stress test" during PET

OBJECTIVE

Visual-processing abnormalities commonly contribute to typical Alzheimer's disease symptoms, but their detailed pathophysiology remains unknown. To investigate why patients with Alzheimer's disease have greater difficulty performing visuoconstructive (magnocellular-dominated) tasks than face- or color-perception (parvocellular-dominated) tasks, the authors measured brain activation in response to a temporally graded visual stimulus (neural stress test) during positron emission tomography.

METHOD

The stress test measured regional cerebral blood flow (CBF) in response to a patterned flash stimulus in the resting state (0 Hz in the dark) and at frequencies of 1, 2, 4, 7, and 14 Hz. Ten patients with Alzheimer's disease and 12 age- and sex-matched comparison subjects were studied.

RESULTS

The striate response at 7 Hz and 14 Hz (the degree of regional CBF increase from that at 0 Hz) was significantly less in the patients than in the comparison subjects, whereas the change in regional CBF at the lower frequencies did not differ between groups. In bilateral middle temporal association areas activated by motion and dominated by magnocellular input, regional CBF at 1 Hz (the frequency with maximal apparent motion) was significantly greater than at 0 Hz in the comparison subjects but not in the patients.

CONCLUSIONS

The magnocellular visual system normally responds to high-frequency input and motion; the failure of response in the striate cortex at high but not low frequencies in the Alzheimer's patients suggests greater magnocellular than parvocellular dysfunction at these levels. Activation failure in the middle temporal areas in the patients supports magnocellular dysfunction. The finding that the Alzheimer's disease group had abnormal visual cortical function emphasizes the importance of clinical visuospatial evaluation of patients with Alzheimer's disease to fully understand symptom production and to plan interventions.

Biomarkers in the age of omics: time for a systems biology approach

Limitations to biomarker discovery are not only technical or bioinformatic but conceptual as well. In our attempt to offer a solution, we are highlighting three issues that we think are limiting progress in biomarkers discovery. First, the confusion stemming from the imposition of a pathology-type immunohistochemical marker (IHCM) concept on omics data without fully understanding the characteristics and limitations of IHCMs as applied in clinical pathology. Second, the lack of serious consideration for the scope of disease heterogeneity. Third, the refusal of the biomedical community to borrow from other biological disciplines their well established methods for dealing with heterogeneity. Therefore, real progress in biomarker discovery will be attained when we recognize that an omics biomarker cannot be assigned and validated without a priori data modeling and subtyping of the disease itself to reveal the extent of its heterogeneity, and its omics' clonal aberrations (drivers) underlying its subtypes and pathways' diversity. To further support our viewpoints, we are contributing a novel a systems biology method such as parsimony phylogenetic approach for disease modeling prior to biomarker circumscription. As an analytical approach that has been successfully used for a half of a century in other biological disciplines, parsimony phylogenetics simultaneously achieves several objectives: it provides disease modeling in a hierarchical phylogenetic classification, identifies biomarkers as the shared derived expressions or mutations--synapomorphies, constructs the omics profiles of specimens based on the most parsimonious arrangement of their heterogeneous data, and permits network profiling of affected signaling pathways as the biosignature of disease classes.

The visual deficit theory of developmental dyslexia

Dyslexia is an impairment in reading that can result from an abnormal developmental process in the case of developmental dyslexia or cerebral insult in the case of acquired dyslexia. It has long been known that the clinical manifestations of developmental dyslexia are varied. In addition to their reading difficulties, individuals with developmental dyslexia exhibit impairments in their ability to process the phonological features of written or spoken language. Recently, it has been demonstrated with a variety of experimental approaches that these individuals are also impaired on a number of visual tasks involving visuomotor, visuospatial, and visual motion processing. The results of these studies, as well as the anatomical and physiological anomalies seen in the brains of individuals with dyslexia, suggest that the pathophysiology of developmental dyslexia is more complex than originally thought, extending beyond the classically defined language areas of the brain. Functional neuroimaging is a useful tool to more precisely delineate the pathophysiology of this reading disorder.

Event-related fast optical signal in a rapid object recognition task: improving detection by the independent component analysis

Noninvasive recording of fast optical signals presumably reflecting neuronal activity is a challenging task because of a relatively low signal-to-noise ratio. To improve detection of those signals in rapid object recognition tasks, we used the independent component analysis (ICA) to reduce "global interference" (heartbeat and contribution of superficial layers). We recorded optical signals from the left prefrontal cortex in 10 right-handed participants with a continuous-wave instrument (DYNOT, NIRx, Brooklyn, NY). Visual stimuli were pictures of urban, landscape and seashore scenes with various vehicles as targets (target-to-non-target ratio 1:6) presented at ISI=166 ms or 250 ms. Subjects mentally counted targets. Data were filtered at 2-30 Hz and artifactual components were identified visually (for heartbeat) and using the ICA weight matrix (for superficial layers). Optical signals were restored from the ICA components with artifactual components removed and then averaged over target and non-target epochs. After ICA processing, the event-related response was detected in 70%-100% of subjects. The refined signal showed a significant decrease from baseline within 200-300 ms after targets and a slight increase after non-targets. The temporal profile of the optical signal corresponded well to the profile of a "differential ERP response", the difference between targets and non-targets which peaks at 200 ms in similar object detection tasks. These results demonstrate that the detection of fast optical responses with continuous-wave instruments can be improved through the ICA method capable to remove noise, global interference and the activity of superficial layers. Fast optical signals may provide further information on brain processing during higher-order cognitive tasks such as rapid categorization of objects.

Exercise challenge in Gulf War Illness reveals two subgroups with altered brain structure and function

Nearly 30% of the approximately 700,000 military personnel who served in Operation Desert Storm (1990-1991) have developed Gulf War Illness, a condition that presents with symptoms such as cognitive impairment, autonomic dysfunction, debilitating fatigue and chronic widespread pain that implicate the central nervous system. A hallmark complaint of subjects with Gulf War Illness is post-exertional malaise; defined as an exacerbation of symptoms following physical and/or mental effort. To study the causal relationship between exercise, the brain, and changes in symptoms, 28 Gulf War veterans and 10 controls completed an fMRI scan before and after two exercise stress tests to investigate serial changes in pain, autonomic function, and working memory. Exercise induced two clinical Gulf War Illness subgroups. One subgroup presented with orthostatic tachycardia (n = 10). This phenotype correlated with brainstem atrophy, baseline working memory compensation in the cerebellar vermis, and subsequent loss of compensation after exercise. The other subgroup developed exercise induced hyperalgesia (n = 18) that was associated with cortical atrophy and baseline working memory compensation in the basal ganglia. Alterations in cognition, brain structure, and symptoms were absent in controls. Our novel findings may provide an understanding of the relationship between the brain and post-exertional malaise in Gulf War Illness.

Functional anatomy of listening and reading comprehension during development

Listening and reading comprehension of paragraph-length material are considered higher-order language skills fundamental to social and academic functioning. Using ecologically relevant language stimuli that were matched for difficulty according to developmental level, we analyze the effects of task, age, neuropsychological skills, and post-task performance on fMRI activation and hemispheric laterality. Areas of supramodal language processing are identified, with the most robust region being left-lateralized activation along the superior temporal sulcus. Functionally, this conjunction has a role in semantic and syntactic processing, leading us to refer to this conjunction as "comprehension cortex." Different from adults, supramodal areas for children include less extensive inferior frontal gyrus but more extensive right cerebellum and right temporal pole. Broader neuroanatomical pathways are recruited for reading, reflecting the more active processing and larger set of cognitive demands needed for reading compared to listening to stories. ROI analyses reveal that reading is a less lateralized language task than listening in inferior frontal and superior temporal areas, which likely reflects the difficulty of the task as children in this study are still developing their reading skills. For listening to stories, temporal activation is stable by age four with no correlations with age, neuropsychological skills or post-task performance. In contrast, frontal activation during listening to stories occurs more often in older children, and frontal activation is positively correlated with better performance on comprehension questions, suggesting that the activation of frontal networks may reflect greater integration and depth of story processing.

Parametric analysis of functional neuroimages: application to a variable-rate motor task

Positron emission tomography (PET) has proven to be a powerful tool in identifying the functional neuroanatomy underlying cognitive and sensorimotor processing. In this paper, we present a method for mathematically modeling the changes in regional cerebral blood flow (rCBF) as a function of experimental parameters using step and linear functions. PET was used to measure rCBF in six subjects who tracked a target moving with constant amplitude across a computer screen at four different frequencies. Each subject tracked the target by flexing and extending the wrist. Two scans were performed at each frequency. The data for each subject were normalized by the mean blood flow in each scan and scaled to the mean blood flow at rest. Scaled rCBF was regressed onto movement frequency to identify voxels which had either a significant linear or step function response to the frequency of movement. A group analysis was also performed to identify significant functional changes common to all subjects. Significant rCBF increases in relation to movement frequency were found in the supplementary motor area, primary motor cortex, premotor cortex, thalamus, and cerebellum and localized using the Talairach atlas. Habituation of responses was not observed.

A prospective study of cognitive fluency and originality in children exposed in utero to carbamazepine, lamotrigine, or valproate monotherapy

OBJECTIVE

To investigate the differential effects of fetal exposure to antiepileptic drugs (AEDs) on cognitive fluency and flexibility in a prospective sample of children.

METHODS

This substudy of the Neurodevelopmental Effects of Antiepileptic Drugs investigation enrolled pregnant women with epilepsy on AED monotherapy (carbamazepine, lamotrigine, and valproate). Blinded to drug exposure, 54 children were tested for ability to generate ideas in terms of quantity (fluency/flexibility) and quality (originality). Forty-two children met inclusion criteria (mean age=4.2 years, SD=0.5) for statistical analyses of drug exposure group differences.

RESULTS

Fluency was lower in the valproate group (mean=76.3, SD=7.53) versus the lamotrigine (mean=93.76, SD=13.5, ANOVA P<0.0015) and carbamazepine (mean=95.5, SD=18.1, ANOVA P<0.003) groups. Originality was lower in the valproate group (mean=84.2, SD=3.23) versus the lamotrigine (mean=103.1, SD=14.8, ANOVA P<0.002) and carbamazepine (mean=99.4, SD=17.1, ANOVA P<0.01) groups. These results were not explained by factors other than AED exposure.

CONCLUSION

Children prenatally exposed to valproate demonstrate impaired fluency and originality compared with children exposed to lamotrigine and carbamazepine.

Contrast-Enhanced In Vivo Imaging of Breast and Prostate Cancer Cells by MRI

The development of effective cancer therapies has been hampered, in part, by the inability to noninvasively follow tumor progression from the initial cancerous lesion through to metastasis. We have previously shown that superparamagnetic iron oxide particles can be used as magnetic resonance imaging contrast agents to label embryonic, mesenchymal and hematopoietic stem cells in vivo. Improving the capacity to non-invasively image cancer progression is an appealing method that could be useful for assessing the efficacy of anticancer therapies. We have established that human prostate (LNCaP, DU145, PC3), rodent prostate (TRAMPC1, YPEN-1), human breast (MDA-MB-231) and mouse mammary (Myc/VEGF) cancer cell lines were readily labeled by fluorescent superparamagnetic sub-micron particles of iron oxide (MPIOs). The MPIOs were essentially inert with respect to cell proliferation and tumor formation. Fluorescence stereomicroscopy and three dimensional magnetic resonance imaging (MRI) determined that subcutaneous, intramuscular or orthotopically implanted labeled cancer cells could be imaged, in vivo, despite in some cases being undetectable by manual palpation. The MPIO-labeled cancer cells could also be imaged, in vivo, at least 6 weeks after implantation. The fluorescent MPIOs further allowed for the ex vivo identification of tumors cells from histological sections. This study demonstrates the feasibility of using fluorescent MPIOs in prostate and breast cancer cell lines as both a negative contrast agent for in vivo MRI as well as a fluorescent tumor marker for optical imaging in vivo and ex vivo.

Cortical regions involved in visual texture perception: a fMRI study

To determine visual areas of the human brain involved in elementary form processing, functional magnetic resonance imaging (fMRI) was used to measure regional responses to two types of achromatic textures. Healthy young adults were presented with 'random' textures which lacked spatial organization of the black and white pixels that make up the image, and 'correlated' textures in which the pixels were ordered to produce extended contours and rectangular blocks at multiple spatial scales. Relative to a fixation condition, random texture stimulation resulted in increased signal intensity primarily in the striate cortex, with slight involvement of the cuneus and middle occipital, lingual and fusiform gyri. Correlated texture stimulation also resulted in activation of these areas, yet the regional extent of this activation was significantly greater than that produced by random textures. Unlike random stimulation, correlated stimulation additionally resulted in middle temporal activation. Direct comparison of the two stimulation conditions revealed significant differences most consistently in the anterior fusiform gyrus, but also in striate, middle occipital, lingual and posterior temporal regions in subjects with robust activation patterns. While both random and correlated stimulation produced activation in similar areas of the occipital lobe, the increase in regional activation during the correlated condition suggests increased recruitment of neuronal populations occurs in response to textures containing visually salient features. This increased recruitment occurs within striate, extrastriate and temporal regions of the brain, also suggesting the presence of receptive field mechanisms in the ventral visual pathway that are sensitive to features produced by higher-order spatial correlations.

Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT): Clinical Applications

Positron emission tomography and single-photon emission computed tomography are nuclear imaging modalities that excel in depicting the biological function of tissue. Unlike structural imaging methods, they provide functional diagnostic information about brain neoplasms, stroke, neurodegenerative disorders, epilepsy, cortical visual loss, and migraine.

Functional connectivity in the prefrontal cortex measured by near-infrared spectroscopy during ultrarapid object recognition

Near-infrared spectroscopy (NIRS) is a developing technology for low-cost noninvasive functional brain imaging. With multichannel optical instruments, it becomes possible to measure not only local changes in hemoglobin concentrations but also temporal correlations of those changes in different brain regions which gives an optical analog of functional connectivity traditionally measured by fMRI. We recorded hemodynamic activity during the Go-NoGo task from 11 right-handed subjects with probes placed bilaterally over prefrontal areas. Subjects were detecting animals as targets in natural scenes pressing a mouse button. Data were low-pass filtered<1 Hz and cardiac∕respiration∕superficial layers artifacts were removed using Independent Component Analysis. Fisher's transformed correlations of poststimulus responses (30 s) were averaged over groups of channels unilaterally in each hemisphere (intrahemispheric connectivity) and the corresponding channels between hemispheres (interhemispheric connectivity). The hemodynamic response showed task-related activation (an increase∕decrease in oxygenated∕deoxygenated hemoglobin, respectively) greater in the right versus left hemisphere. Intra- and interhemispheric functional connectivity was also significantly stronger during the task compared to baseline. Functional connectivity between the inferior and the middle frontal regions was significantly stronger in the right hemisphere. Our results demonstrate that optical methods can be used to detect transient changes in functional connectivity during rapid cognitive processes.