Measuring the thickness of the human cerebral cortex from magnetic resonance images

Accurate and automated methods for measuring the thickness of human cerebral cortex could provide powerful tools for diagnosing and studying a variety of neurodegenerative and psychiatric disorders. Manual methods for estimating cortical thickness from neuroimaging data are labor intensive, requiring several days of effort by a trained anatomist. Furthermore, the highly folded nature of the cortex is problematic for manual techniques, frequently resulting in measurement errors in regions in which the cortical surface is not perpendicular to any of the cardinal axes. As a consequence, it has been impractical to obtain accurate thickness estimates for the entire cortex in individual subjects, or group statistics for patient or control populations. Here, we present an automated method for accurately measuring the thickness of the cerebral cortex across the entire brain and for generating cross-subject statistics in a coordinate system based on cortical anatomy. The intersubject standard deviation of the thickness measures is shown to be less than 0.5 mm, implying the ability to detect focal atrophy in small populations or even individual subjects. The reliability and accuracy of this new method are assessed by within-subject test-retest studies, as well as by comparison of cross-subject regional thickness measures with published values.

Functional imaging of brain responses to pain. A review and meta-analysis (2000)

Brain responses to pain, assessed through positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) are reviewed. Functional activation of brain regions are thought to be reflected by increases in the regional cerebral blood flow (rCBF) in PET studies, and in the blood oxygen level dependent (BOLD) signal in fMRI. rCBF increases to noxious stimuli are almost constantly observed in second somatic (SII) and insular regions, and in the anterior cingulate cortex (ACC), and with slightly less consistency in the contralateral thalamus and the primary somatic area (SI). Activation of the lateral thalamus, SI, SII and insula are thought to be related to the sensory-discriminative aspects of pain processing. SI is activated in roughly half of the studies, and the probability of obtaining SI activation appears related to the total amount of body surface stimulated (spatial summation) and probably also by temporal summation and attention to the stimulus. In a number of studies, the thalamic response was bilateral, probably reflecting generalised arousal in reaction to pain. ACC does not seem to be involved in coding stimulus intensity or location but appears to participate in both the affective and attentional concomitants of pain sensation, as well as in response selection. ACC subdivisions activated by painful stimuli partially overlap those activated in orienting and target detection tasks, but are distinct from those activated in tests involving sustained attention (Stroop, etc.). In addition to ACC, increased blood flow in the posterior parietal and prefrontal cortices is thought to reflect attentional and memory networks activated by noxious stimulation. Less noted but frequent activation concerns motor-related areas such as the striatum, cerebellum and supplementary motor area, as well as regions involved in pain control such as the periaqueductal grey. In patients, chronic spontaneous pain is associated with decreased resting rCBF in contralateral thalamus, which may be reverted by analgesic procedures. Abnormal pain evoked by innocuous stimuli (allodynia) has been associated with amplification of the thalamic, insular and SII responses, concomitant to a paradoxical CBF decrease in ACC. It is argued that imaging studies of allodynia should be encouraged in order to understand central reorganisations leading to abnormal cortical pain processing. A number of brain areas activated by acute pain, particularly the thalamus and anterior cingulate, also show increases in rCBF during analgesic procedures. Taken together, these data suggest that hemodynamic responses to pain reflect simultaneously the sensory, cognitive and affective dimensions of pain, and that the same structure may both respond to pain and participate in pain control. The precise biochemical nature of these mechanisms remains to be investigated.

Subcortical and cortical brain activity during the feeling of self-generated emotions

In a series of [15O]PET experiments aimed at investigating the neural basis of emotion and feeling, 41 normal subjects recalled and re-experienced personal life episodes marked by sadness, happiness, anger or fear. We tested the hypothesis that the process of feeling emotions requires the participation of brain regions, such as the somatosensory cortices and the upper brainstem nuclei, that are involved in the mapping and/or regulation of internal organism states. Such areas were indeed engaged, underscoring the close relationship between emotion and homeostasis. The findings also lend support to the idea that the subjective process of feeling emotions is partly grounded in dynamic neural maps, which represent several aspects of the organism's continuously changing internal state.

Functional neuroanatomy of face and object processing. A positron emission tomography study

Studies of brain-damaged patients have revealed the existence of a selective impairment of face processing, prosopagnosia, resulting from lesions at different loci in the occipital and temporal lobes. The results of such studies have led to the identification of several cortical areas underlying the processing of faces, but it remains unclear what functional aspects of face processing are served by these areas and whether they are uniquely devoted to the processing of faces. The present study addresses these questions in a positron emission tomography (PET) study of regional cerebral blood flow in normal adults, using the 15 oxygen water bolus technique. The subjects participated in six tasks (with gratings, faces and objects), and the resulting level of cerebral activation was mapped on images of the subjects' cerebral structures obtained through magnetic resonance and was compared between tasks using the subtraction method. Compared with a fixation condition, regional cerebral blood flow (rCBF) changes were found in the striate and extrastriate cortex when subjects had to decide on the orientation of sine-wave gratings. A face-gender categorization resulted in activation changes in the right extrastriate cortex, and a face-identity condition produced additional activation of the fusiform gyrus and anterior temporal cortex of both hemispheres, and of the right parahippocampal gyrus and adjacent areas. Cerebral activation during an object-recognition task occurred essentially in the left occipito-temporal cortex and did not involve the right hemisphere regions specifically activated during the face-identity task. The results provide the first empirical evidence from normal subjects regarding the crucial role of the ventro-medial region of the right hemisphere in face recognition, and they offer new information about the dissociation between face and object processing.

Practice-related changes in human brain functional anatomy during nonmotor learning

Practice of a novel task leads to improved performance. The brain mechanisms associated with practice-induced improvement in performance are largely unknown. To address this question we have examined the functional anatomy of the human brain with positron emission tomography (PET) during the naive and practiced performance of a simple verbal response selection task (saying an appropriate verb for a visually presented noun). As a control state, subjects were asked to repeat the visually presented nouns. Areas of the brain most active during naive performance (anterior cingulate, left prefrontal and left posterior temporal cortices, and the right cerebellar hemisphere), compared to repeating the visually presented nouns, were all significantly less active during practiced performance. These changes were accompanied by changes in the opposite direction in sylvian-insular cortex bilaterally and left medial extrastriate cortex. In effect, brief practice made the cortical circuitry used for verbal response selection indistinguishable from simple word repetition. Introduction of a novel list of words reversed the learning-related effects. These results indicate that two distinct circuits can be used for verbal response selection and normal subjects can change the brain circuits used during task performance following less than 15 min of practice. One critical factor in determining the circuitry used appears to be the degree to which a task is learned or automatic.

Cortical abnormalities in adults and adolescents with major depression based on brain scans from 20 cohorts worldwide in the ENIGMA Major Depressive Disorder Working Group

The neuro-anatomical substrates of major depressive disorder (MDD) are still not well understood, despite many neuroimaging studies over the past few decades. Here we present the largest ever worldwide study by the ENIGMA (Enhancing Neuro Imaging Genetics through Meta-Analysis) Major Depressive Disorder Working Group on cortical structural alterations in MDD. Structural T1-weighted brain magnetic resonance imaging (MRI) scans from 2148 MDD patients and 7957 healthy controls were analysed with harmonized protocols at 20 sites around the world. To detect consistent effects of MDD and its modulators on cortical thickness and surface area estimates derived from MRI, statistical effects from sites were meta-analysed separately for adults and adolescents. Adults with MDD had thinner cortical gray matter than controls in the orbitofrontal cortex (OFC), anterior and posterior cingulate, insula and temporal lobes (Cohen's d effect sizes: -0.10 to -0.14). These effects were most pronounced in first episode and adult-onset patients (>21 years). Compared to matched controls, adolescents with MDD had lower total surface area (but no differences in cortical thickness) and regional reductions in frontal regions (medial OFC and superior frontal gyrus) and primary and higher-order visual, somatosensory and motor areas (d: -0.26 to -0.57). The strongest effects were found in recurrent adolescent patients. This highly powered global effort to identify consistent brain abnormalities showed widespread cortical alterations in MDD patients as compared to controls and suggests that MDD may impact brain structure in a highly dynamic way, with different patterns of alterations at different stages of life.

Thermosensory activation of insular cortex

Temperature sensation is regarded as a submodality of touch, but evidence suggests involvement of insular cortex rather than parietal somatosensory cortices. Using positron emission tomography (PET), we found contralateral activity correlated with graded cooling stimuli only in the dorsal margin of the middle/posterior insula in humans. This corresponds to the thermoreceptive- and nociceptive-specific lamina I spinothalamocortical pathway in monkeys, and can be considered an enteroceptive area within limbic sensory cortex. Because lesions at this site can produce the post-stroke central pain syndrome, this finding supports the proposal that central pain results from loss of the normal inhibition of pain by cold. Notably, perceived thermal intensity was well correlated with activation in the right (ipsilateral) anterior insular and orbitofrontal cortices.

Self-initiated versus externally triggered movements. I. An investigation using measurement of regional cerebral blood flow with PET and movement-related potentials in normal and Parkinson's disease subjects

We investigated the functional anatomy of self-initiated and externally triggered movements. Six patients with Parkinson's disease off medication and six age-matched normals were assessed. All subjects had regional cerebral blood flow (rCBF) measurement with PET and recording of movement-related cortical potentials (MRPs) from frontal (F), fronto-central (FC), central (C) and parietal (P) sites to obtain measures of the Bereitschaftspotential (BP). The tasks were (i) self-initiated extension of the right index finger on average once every 3 s, (ii) externally triggered finger extension with the rate yoked to the self-initiated task, and (iii) rest condition with tones presented at a rate yoked with the self-initiated task. For the self-initiated movements, the amplitude of the early and peak BP were lower in Parkinson's disease relative to normals. For the externally triggered movements, the patients and the normals did not differ on any of the measures of cortical negativity prior to movement. For both groups, the late and peak BP components, but not the early component, had a lower amplitude in the externally triggered than the self-initiated movements. In normals, the left primary sensorimotor cortex, the supplementary motor area bilaterally, anterior cingulate, the lateral premotor cortex bilaterally, the insular cortex bilaterally, the left thalamus and the left putamen, parietal area 40 bilaterally and the right dorsolateral prefrontal cortex (DLPFC) were significantly activated during the self-initiated movements relative to rest. For the normals, greater activation of the right DLPFC during the self-initiated movements was the only area that significantly differentiated them from the externally triggered movements. When Parkinson's disease patients and normals were compared for the self-initiated movements relative to rest, normals showed greater activation of the supplementary motor area and anterior cingulate, left putamen, left insular cortex, right DLPFC and right parietal area 40. When the groups were compared for the externally triggered movements relative to rest, the global pattern of blood flow and rCBF change in the two groups did not differ, confirming the absence of group differences in BPs for the externally triggered movements. During the self-initiated movements, the lower amplitude of the early BP in patients with Parkinson's disease as well as the underactivation of the supplementary motor area relative to normals support the premises that (i) the supplementary motor area contributes to the early BP, and (ii) the deficit is self-initiated movements in Parkinson's disease is due to supplementary motor area underactivation. The DLPFC is activated in situations requiring non-routine decision making as in the self-initiated movements.

Modulation of cortical-limbic pathways in major depression: treatment-specific effects of cognitive behavior therapy

BACKGROUND

Functional imaging studies of major depressive disorder demonstrate response-specific regional changes following various modes of antidepressant treatment.

OBJECTIVE

To examine changes associated with cognitive behavior therapy (CBT).

METHODS

Brain changes underlying response to CBT were examined using resting-state fluorine-18-labeled deoxyglucose positron emission tomography. Seventeen unmedicated, unipolar depressed outpatients (mean +/- SD age, 41 +/- 9 years; mean +/- SD initial 17-item Hamilton Depression Rating Scale score, 20 +/- 3) were scanned before and after a 15- to 20-session course of outpatient CBT. Whole-brain, voxel-based methods were used to assess response-specific CBT effects. A post hoc comparison to an independent group of 13 paroxetine-treated responders was also performed to interpret the specificity of identified CBT effects.

RESULTS

A full course of CBT resulted in significant clinical improvement in the 14 study completers (mean +/- SD posttreatment Hamilton Depression Rating Scale score of 6.7 +/- 4). Treatment response was associated with significant metabolic changes: increases in hippocampus and dorsal cingulate (Brodmann area [BA] 24) and decreases in dorsal (BA 9/46), ventral (BA 47/11), and medial (BA 9/10/11) frontal cortex. This pattern is distinct from that seen with paroxetine-facilitated clinical recovery where prefrontal increases and hippocampal and subgenual cingulate decreases were seen.

CONCLUSIONS

Like other antidepressant treatments, CBT seems to affect clinical recovery by modulating the functioning of specific sites in limbic and cortical regions. Unique directional changes in frontal cortex, cingulate, and hippocampus with CBT relative to paroxetine may reflect modality-specific effects with implications for understanding mechanisms underlying different treatment strategies.

Mapping motor representations with positron emission tomography

Brain activity was mapped in normal subjects during passive observation of the movements of an 'alien' hand and while imagining grasping objects with their own hand. None of the tasks required actual movement. Shifting from one mental task to the other greatly changed the pattern of brain activation. During observation of hand movements, activation was mainly found in visual cortical areas, but also in subcortical areas involved in motor behaviour, such as the basal ganglia and the cerebellum. During motor imagery, cortical and subcortical areas related to motor preparation and programming were strongly activated. These data support the notion that motor learning during observation of movements and mental practice involves rehearsal of neural pathways related to cognitive stages of motor control.

Cortical areas and the selection of movement: a study with positron emission tomography

Regional cerebral blood flow was measured in normal subjects with positron emission tomography (PET) while they performed five different motor tasks. In all tasks they had to moved a joystick on hearing a tone. In the control task they always pushed it forwards (fixed condition), and in four other experimental tasks the subjects had to select between four possible directions of movement. These four tasks differed in the basis for movement selection. A comparison was made between the regional blood flow for the four tasks involving movement selection and the fixed condition in which no selection was required. When selection of a movement was made, significant increases in regional cerebral blood flow were found in the premotor cortex, supplementary motor cortex, and superior parietal association cortex. A comparison was also made between the blood flow maps generated when subjects performed tasks based on internal or external cues. In the tasks with internal cues the subjects could prepare their movement before the trigger stimulus, whereas in the tasks with external cues they could not. There was greater activation in the supplementary motor cortex for the tasks with internal cues. Finally a comparison was made between each of the selection conditions and the fixed condition; the greatest and most widespread changes in regional activity were generated by the task on which the subjects themselves made a random selection between the four movements.

Willed action and the prefrontal cortex in man: a study with PET

We used positron emission tomography to contrast changes in cerebral blood flow associated with willed and routine acts. In the six tasks used, volunteers had to make a series of responses to a sequence of stimuli. For the routine acts, each response was completely specified by the stimulus. For the willed acts, the response was open-ended and therefore volunteers had to make a deliberate choice. Willed acts in the two response modalities studied (speaking a word, or lifting a finger) were associated with increased blood flow in the dorsolateral prefrontal cortex (Brodmann area 46). Willed acts were also associated with decreases in blood flow, but the location of these decreases was modality dependent.

Object and spatial visual working memory activate separate neural systems in human cortex

Human and nonhuman primate visual systems are divided into object and spatial information processing pathways. In the macaque, it has been shown that these pathways project to separate areas in the frontal lobe and that the ventral and dorsal frontal areas are, respectively, involved in working memory for objects and spatial locations. A positron emission tomography (PET) study was done to determine if a similar anatomical segregation exists in humans for object and spatial visual working memory. Face working memory demonstrated significant increases in regional cerebral blood flow (rCBF), relative to location working memory, in fusiform, parahippocampal, inferior frontal, and anterior cingulate cortices, and in right thalamus and midline cerebellum. Location working memory demonstrated significant increases in cRBF, relative to face working memory, in superior and inferior parietal cortex, and in the superior frontal sulcus. Our results show that the neural systems involved in working memory for faces and for spatial location are functionally segregated, with different areas recruited in both extrastriate and frontal cortices for processing the two types of visual information.

Distribution of cortical neural networks involved in word comprehension and word retrieval

Six normal volunteers were studied with positron emission tomography to identify the cortical neural networks that participate in the processing of single words. Activity-related changes in regional cerebral blood flow were measured consecutively on 6 occasions in each subject, 2 while the subject was at rest and 4 while single word language tasks were being performed. The data from each subject were standardized for brain shape and size, reconstructed parallel to the intercommissural line, normalized for global flow differences, and then averaged for each activation condition across the 6 subjects. Significant areas of change in rCBF (P less than 0.05, with appropriate Bonferroni corrections) between task and rest conditions were displayed with reference to the coordinates of a standard neuroanatomical atlas. We have demonstrated that categorical judgements on heard pairs of real words activate neural networks along both superior temporal gyri, but with an anatomical distribution no different from that seen when the subjects listened to nonwords: the tasks would appear to be very different in cognitive demands but not in terms of the distribution of activation. However, during a verb generation task that involved thinking of verbs appropriate to heard nouns presented at a slow rate, the only temporal region activated was the left posterior superior temporal association cortex (Wernicke's area). Further analysis showed that whereas activation in other superior temporal regions, both left and right, correlated with rates of word presentation during the 4 tasks, there was no such correlation in Wernicke's area; evidence that this site is responsible for more than early acoustic processing. During verb generation there was also activation of left premotor and prefrontal cortex (including Broca's area and the supplementary motor area). The supplementary motor area is thought to be involved in the motor planning of speech. The subjects did not vocalize during the task, and therefore it would appear that the act of retrieving words from semantic memory activates networks concerned with the production of speech sounds. We conclude that single word comprehension and retrieval activate very different distributed regions of cerebral cortex, with Wernicke's area the only region engaged by both processes and with participation during silent word generation of networks involved in vocalization.

Large-Scale Gradients in Human Cortical Organization

Recent advances in mapping cortical areas in the human brain provide a basis for investigating the significance of their spatial arrangement. Here we describe a dominant gradient in cortical features that spans between sensorimotor and transmodal areas. We propose that this gradient constitutes a core organizing axis of the human cerebral cortex, and describe an intrinsic coordinate system on its basis. Studying the cortex with respect to these intrinsic dimensions can inform our understanding of how the spectrum of cortical function emerges from structural constraints.

Individual patterns of functional reorganization in the human cerebral cortex after capsular infarction

We have previously shown bilateral activation of motor pathways and the recruitment of additional motor areas in studies of groups of patients with recovery from motor stroke. We have now developed a new positron emission tomographic technique to measure the changes in regional cerebral blood flow elicited during a motor task in individual patients, relative to the cerebral activation found in normal subjects. The patterns of cerebral activation in each of 8 individual patients with capsular lesions of the pyramidal tract and complete recovery from hemiplegia are described by comparison with the pattern found in a representative sample of 10 normal subjects. We found a large ventral extension of the hand field of the contralateral (sensori)motor cortex in all patients with lesions of the posterior limb of the internal capsule. Greater activation than in normal subjects was found in variable combinations of the supplementary motor areas, the insula, the frontal operculum, and the parietal cortex. Structures belonging to motor pathways ipsilateral to the recovered limb were also more activated in the patients than in normal subjects. However, additional activation of the ipsilateral (sensori)motor cortex was only found in the 4 patients who exhibited associated movements of the unaffected hand when the recovered hand performed the motor task. We conclude that recovery from motor stroke due to striatocapsular damage is associated with individually different patterns of functional reorganization of the brain. These patterns are dependent on the site of the subcortical lesion and the somatotopic organization of the pyramidal tract, both of which may determine the precise potential for recovery of limb function following this type of brain injury.

Local cerebral glucose metabolic rates in obsessive-compulsive disorder. A comparison with rates in unipolar depression and in normal controls

We studied 14 patients with obsessive-compulsive disorder (OCD) by positron emission tomography and the fluorodeoxyglucose method, looking for abnormalities in local cerebral metabolic rates for glucose in brain structures that have been hypothesized to function abnormally in OCD. These patients were compared with 14 normal controls and 14 patients with unipolar depression. The patients with unipolar depression and OCD did not differ in levels of anxiety, tension, or depression. In OCD, metabolic rates were significantly increased in the left orbital gyrus and bilaterally in the caudate nuclei. This was apparent on all statistical comparisons with both controls and unipolar depression. The right orbital gyrus showed at least a trend to an increased metabolic rate in all comparisons. The metabolic rate in the left orbital gyrus, relative to that in the ipsilateral hemisphere (orbital gyrus/hemisphere ratio), was significantly elevated compared to controls and subjects with unipolar depression, and stayed high even with successful drug treatment. Though it was in the normal range in the morbid state, with improvement in OCD symptoms after drug treatment, the caudate/hemisphere metabolic ratio increased uniformly and significantly bilaterally. This ratio did not increase in patients who did not respond to treatment. Thus, OCD showed cerebral glucose metabolic patterns that differed from controls in both the symptomatic and recovered states.

PET imaging of amyloid deposition in patients with mild cognitive impairment

It is of great clinical value to identify subjects at a high risk of developing AD. We previously found that the amyloid positron emission tomography (PET) tracer PIB showed a robust difference in retention in the brain between AD patients and healthy controls (HC). Twenty-one patients diagnosed with MCI (mean age 63.3+/-7.8 (S.D.) years) underwent PET studies with (11)C-PIB, and (18)F-fluoro-deoxy-glucose (FDG) to measure cerebral glucose metabolism, as well as assessment of cognitive function and CSF sampling. Reference group data from 27 AD patients and 6 healthy controls, respectively, were used for comparison. The mean cortical PIB retention for the MCI patients was intermediate compared to HC and AD. Seven MCI patients that later at clinical follow-up converted to AD (8.1+/-6.0 (S.D.) months) showed significant higher PIB retention compared to non-converting MCI patients and HC, respectively (ps<0.01). The PIB retention in MCI converters was comparable to AD patients (p>0.01). Correlations were observed in the MCI patients between PIB retention and CSF Abeta(1-42), total Tau and episodic memory, respectively.

Modulating the experience of agency: a positron emission tomography study

This study investigated agency, the feeling of being causally involved in an action. This is the feeling that leads us to attribute an action to ourselves rather than to another person. We were interested in the effects of experimentally modulating this experience on brain areas known to be involved in action recognition and self-recognition. We used a device that allowed us to modify the subject's degree of control of the movements of a virtual hand presented on a screen. Four main conditions were used: (1) a condition where the subject had a full control of the movements of the virtual hand, (2) a condition where the movements of the virtual hand appeared rotated by 25 degrees with respect to the movements made by the subject, (3) a condition where the movements of the virtual hand appeared rotated by 50 degrees, and (4) a condition where the movements of the virtual hand were produced by another person and did not correspond to the subject's movements. The activity of two main brain areas appeared to be modulated by the degree of discrepancy between the movement executed and the movement seen on the screen. In the inferior part of the parietal lobe, specifically on the right side, the less the subject felt in control of the movements of the virtual hand, the higher the level of activation. A reverse covariation was observed in the insula. These results demonstrate that the level of activity of specific brain areas maps onto the experience of causing or controlling an action. The implication of these results for understanding pathological conditions is discussed.

Four distinct trajectories of tau deposition identified in Alzheimer's disease

Alzheimer's disease (AD) is characterized by the spread of tau pathology throughout the cerebral cortex. This spreading pattern was thought to be fairly consistent across individuals, although recent work has demonstrated substantial variability in the population with AD. Using tau-positron emission tomography scans from 1,612 individuals, we identified 4 distinct spatiotemporal trajectories of tau pathology, ranging in prevalence from 18 to 33%. We replicated previously described limbic-predominant and medial temporal lobe-sparing patterns, while also discovering posterior and lateral temporal patterns resembling atypical clinical variants of AD. These 'subtypes' were stable during longitudinal follow-up and were replicated in a separate sample using a different radiotracer. The subtypes presented with distinct demographic and cognitive profiles and differing longitudinal outcomes. Additionally, network diffusion models implied that pathology originates and spreads through distinct corticolimbic networks in the different subtypes. Together, our results suggest that variation in tau pathology is common and systematic, perhaps warranting a re-examination of the notion of 'typical AD' and a revisiting of tau pathological staging.

The functional neuroanatomy of the placebo effect

OBJECTIVE

Administration of placebo can result in a clinical response indistinguishable from that seen with active antidepressant treatment. Functional brain correlates of this phenomenon have not been fully characterized.

METHOD

Changes in brain glucose metabolism were measured by using positron emission tomography in hospitalized men with unipolar depression who were administered placebo as part of an inpatient imaging study of fluoxetine. Common and unique response effects to administration of placebo or fluoxetine were assessed after a 6-week, double-blind trial.

RESULTS

Placebo response was associated with regional metabolic increases involving the prefrontal, anterior cingulate, premotor, parietal, posterior insula, and posterior cingulate and metabolic decreases involving the subgenual cingulate, parahippocampus, and thalamus. Regions of change overlapped those seen in responders administered active fluoxetine. Fluoxetine response, however, was associated with additional subcortical and limbic changes in the brainstem, striatum, anterior insula, and hippocampus, sources of efferent input to the response-specific regions identified with both agents.

CONCLUSIONS

The common pattern of cortical glucose metabolism increases and limbic-paralimbic metabolism decreases in placebo and fluoxetine responders suggests that facilitation of these changes may be necessary for depression remission, regardless of treatment modality. Clinical improvement in the group receiving placebo as part of an inpatient study is consistent with the well-recognized effect that altering the therapeutic environment may significantly contribute to reducing clinical symptoms. The additional subcortical and limbic metabolism decreases seen uniquely in fluoxetine responders may convey additional advantage in maintaining long-term clinical response and in relapse prevention.

Age-related reductions in human recognition memory due to impaired encoding

The participation of the medial temporal cortex and other cerebral structures in the memory impairment that accompanies aging was examined by means of positron emission tomography. Cerebral blood flow (rCBF) was measured during encoding and recognition of faces. Young people showed increased rCBF in the right hippocampus and the left prefrontal and temporal cortices during encoding and in the right prefrontal and parietal cortex during recognition. Old people showed no significant activation in areas activated during encoding in young people but did show right prefrontal activation during recognition. Age-related impairments of memory may be due to a failure to encode the stimuli adequately, which is reflected in the lack of cortical and hippocampal activation during encoding.

Functional brain correlates of social and nonsocial processes in autism spectrum disorders: an activation likelihood estimation meta-analysis

BACKGROUND

Functional neuroimaging studies of autism spectrum disorders (ASD) have examined social and nonsocial paradigms, although rarely in the same study. Here, we provide an objective, unbiased survey of functional brain abnormalities in ASD, related to both social and nonsocial processing.

METHODS

We conducted two separate voxel-wise activation likelihood estimation meta-analyses of 39 functional neuroimaging studies consisting of 24 studies examining social processes (e.g., theory of mind, face perception) and 15 studies examining nonsocial processes (e.g., attention control, working memory). Voxel-wise significance threshold was p<.05, corrected by false discovery rate.

RESULTS

Compared with neurotypical control (NC) subjects, ASD showed greater likelihood of hypoactivation in two medial wall regions: perigenual anterior cingulate cortex (ACC) in social tasks only and dorsal ACC in nonsocial studies. Further, right anterior insula, recently linked to social cognition, was more likely to be hypoactivated in ASD in the analyses of social studies. In nonsocial studies, group comparisons showed greater likelihood of activation for the ASD group in the rostral ACC region that is typically suppressed during attentionally demanding tasks.

CONCLUSIONS

Despite substantial heterogeneity of tasks, the rapidly increasing functional imaging literature showed ASD-related patterns of hypofunction and aberrant activation that depended on the specific cognitive domain, i.e., social versus nonsocial. These results provide a basis for targeted extensions of these findings with younger subjects and a range of paradigms, including analyses of default mode network regulation in ASD.

Infantile spasms: I. PET identifies focal cortical dysgenesis in cryptogenic cases for surgical treatment

Positron emission tomography (PET) of local cerebral glucose metabolism in 13 children with infantile spasms of undetermined cause (cryptogenic spasms) revealed unilateral hypometabolism involving the parieto-occipito-temporal region in 5 female infants. Cranial computed tomography showed normal findings in all infants. Magnetic resonance imaging (MRI) demonstrated a normal appearance in 4 of the 5 infants; in 1 infant, MRI revealed a subtle abnormality consisting of poor demarcation between occipital gray and white matter. Surface electroencephalography (EEG) in 4 showed hypsarrythmia at some time in the patients' courses, but at other times showed localized or lateralized abnormalities corresponding to areas of PET-detected hypometabolism. Because of poor seizure control, 4 infants underwent surgical removal of the cortical focus guided by intraoperative electrocorticography and were seizure free postoperatively. Neuropathological examination of resected tissue in each showed microscopic cortical dysplasia. Our findings indicate that in infants with cryptogenic spasms, PET can effectively identify those due to unsuspected focal cortical dysplasia, for which resective surgery offers improved prognosis.