Hemispheric specialization in human dorsal frontal cortex and medial temporal lobe for verbal and nonverbal memory encoding

Differential patterns of prefrontal MEG activation during verbal & visual encoding and retrieval

The spatiotemporal profile of activation of the prefrontal cortex in verbal and non-verbal recognition memory was examined using magnetoencephalography (MEG). Sixteen neurologically healthy right-handed participants were scanned whilst carrying out a modified version of the Doors and People Test of recognition memory. A pattern of significant prefrontal activity was found for non-verbal and verbal encoding and recognition. During the encoding, verbal stimuli activated an area in the left ventromedial prefrontal cortex, and non-verbal stimuli activated an area in the right. A region in the left dorsolateral prefrontal cortex also showed significant activation during the encoding of non-verbal stimuli. Both verbal and non-verbal stimuli significantly activated an area in the right dorsomedial prefrontal cortex and the right anterior prefrontal cortex during successful recognition, however these areas showed temporally distinct activation dependent on material, with non-verbal showing activation earlier than verbal stimuli. Additionally, non-verbal material activated an area in the left anterior prefrontal cortex during recognition. These findings suggest a material-specific laterality in the ventromedial prefrontal cortex during encoding for verbal and non-verbal but also support the HERA model for verbal material. The discovery of two process dependent areas during recognition that showed patterns of temporal activation dependent on material demonstrates the need for the application of more temporally sensitive techniques to the involvement of the prefrontal cortex in recognition memory.

Amyloid-β load predicts medial temporal lobe dysfunction in Alzheimer dementia

Amyloid-β (Aβ) deposition is a pathologic hallmark of Alzheimer disease (AD). Although the typical spatial distribution pattern of Aβ deposition in early AD mainly involves regions distant from the hippocampus, the predominant clinical feature is impairment of hippocampus-dependent memory. We aimed at elucidating the relationship between neocortical Aβ load, regional neuronal function, and memory impairment.

METHODS

Thirty patients with early AD underwent combined (11)C-Pittsburgh compound B ((11)C-PIB) and (18)F-FDG PET and memory assessments. Composite measures of hemispheric Aβ load were calculated by volume-weighted mean values of neocortical (11)C-PIB binding. Voxelwise (18)F-FDG uptake was used as a measure of regional glucose metabolism reflecting neuronal activity. We investigated the relationship between left- and right-hemispheric Aβ load and regional glucose metabolism (voxelwise analyses). In addition, we assessed the correlations of hemispheric Aβ load (region-of-interest-based analyses) and regional glucose metabolism (voxelwise analysis) with memory performance. Analyses were corrected for age and sex.

RESULTS

Higher Aβ load in the left hemisphere was associated with reduced glucose metabolism of the left medial temporal lobe (MTL; r(2) = 0.38) and correlated with worse wordlist recall (r = -0.37; partial correlation controlled for sex and age). Furthermore, wordlist recall correlated with regional glucose metabolism in the bilateral MTL and precuneus-posterior cingulate cortex and right lingual gyrus (r(2) = 0.24).

CONCLUSION

We demonstrated an association between the left-hemispheric Aβ load and impairment of the left MTL in AD at 2 different levels: regional hypometabolism and verbal memory. This correlation suggests that neocortical amyloid deposition is connected to or even drives neuronal dysfunction and neurodegeneration of the MTL, which is associated with impaired episodic memory processing as a clinical core symptom of AD.

Explorations of object and location memory using fMRI

Content-specific sub-systems of visual working memory (VWM) have been explored in many neuroimaging studies with inconsistent findings and procedures across experiments. The present study employed functional magnetic resonance imaging (fMRI) and a change detection task using a high number of trials and matched stimulus displays across object and location change (what vs. where) conditions. Furthermore, individual task periods were studied independently across conditions to identify differences corresponding to each task period. Importantly, this combination of task controls has not previously been described in the fMRI literature. Composite results revealed differential frontoparietal activation during each task period. A separation of object and location conditions yielded a distributed system of dorsal and ventral streams during the encoding of information corresponding to bilateral inferior parietal lobule (IPL) and lingual gyrus activation, respectively. Differential activity was also shown during the maintenance of information in middle frontal structures bilaterally for objects and the right IPL and left insula for locations. Together, these results reflect a domain-specific dissociation spanning several cortices and task periods. Furthermore, differential activations suggest a general caudal-rostral separation corresponding to object and location memory, respectively.

Functional organization and visual representations of human ventral lateral prefrontal cortex

Recent neuroimaging studies in both human and non-human primates have identified face selective activation in the ventral lateral prefrontal cortex (VLPFC) even in the absence of working memory (WM) demands. Further, research has suggested that this face-selective response is largely driven by the presence of the eyes. However, the nature and origin of visual category responses in the VLPFC remain unclear. In a broader sense, how do these findings relate to our current understandings of lateral prefrontal cortex? What do these findings tell us about the underlying function and organization principles of the VLPFC? What is the future direction for investigating visual representations in this cortex? This review focuses on the function, topography, and circuitry of the VLPFC to enhance our understanding of the evolution and development of this cortex.

COMT influences on prefrontal and striatal blood oxygenation level-dependent responses during working memory among individuals with schizophrenia, their siblings, and healthy controls

INTRODUCTION

Recent theories have suggested that corticostriatal interactions may play an important part in mediating working memory demands and may impact clinical symptomology of schizophrenia. These effects are thought to occur through changes in dopamine signalling from the midbrain and via feedback from the frontal cortex. The catechol-O-methyltransferase (COMT) Val158Met polymorphism may prove useful for studying these effects in vivo.

METHODS

In this study, patients with schizophrenia, their well siblings, and healthy controls were genotyped and scanned using functional magnetic resonance imaging (fMRI) while they performed a working memory task.

RESULTS

We found that patients and their siblings, but not controls, who were Val homozygotes displayed greater activity of the DLPFC, striatum, and the cerebellum during the task than respective Met carriers. We also found a relationship between striatal activity and negative symptoms for the Val homozygote group.

CONCLUSIONS

Our findings support and extend previous studies of COMT effects on cognition and neural activity, and suggest that changes in dopamine availability may differentially impact corticostriatal functioning of individuals at risk for schizophrenia from those who are not. We also found some evidence supporting the proposed role of striatal dopamine signalling and clinical symptoms associated with anhedonia and apathy.

A functional magnetic resonance imaging study mapping the episodic memory encoding network in temporal lobe epilepsy

Functional magnetic resonance imaging has demonstrated reorganization of memory encoding networks within the temporal lobe in temporal lobe epilepsy, but little is known of the extra-temporal networks in these patients. We investigated the temporal and extra-temporal reorganization of memory encoding networks in refractory temporal lobe epilepsy and the neural correlates of successful subsequent memory formation. We studied 44 patients with unilateral temporal lobe epilepsy and hippocampal sclerosis (24 left) and 26 healthy control subjects. All participants performed a functional magnetic resonance imaging memory encoding paradigm of faces and words with subsequent out-of-scanner recognition assessments. A blocked analysis was used to investigate activations during encoding and neural correlates of subsequent memory were investigated using an event-related analysis. Event-related activations were then correlated with out-of-scanner verbal and visual memory scores. During word encoding, control subjects activated the left prefrontal cortex and left hippocampus whereas patients with left hippocampal sclerosis showed significant additional right temporal and extra-temporal activations. Control subjects displayed subsequent verbal memory effects within left parahippocampal gyrus, left orbitofrontal cortex and fusiform gyrus whereas patients with left hippocampal sclerosis activated only right posterior hippocampus, parahippocampus and fusiform gyrus. Correlational analysis showed that patients with left hippocampal sclerosis with better verbal memory additionally activated left orbitofrontal cortex, anterior cingulate cortex and left posterior hippocampus. During face encoding, control subjects showed right lateralized prefrontal cortex and bilateral hippocampal activations. Patients with right hippocampal sclerosis showed increased temporal activations within the superior temporal gyri bilaterally and no increased extra-temporal areas of activation compared with control subjects. Control subjects showed subsequent visual memory effects within right amygdala, hippocampus, fusiform gyrus and orbitofrontal cortex. Patients with right hippocampal sclerosis showed subsequent visual memory effects within right posterior hippocampus, parahippocampal and fusiform gyri, and predominantly left hemisphere extra-temporal activations within the insula and orbitofrontal cortex. Correlational analysis showed that patients with right hippocampal sclerosis with better visual memory activated the amygdala bilaterally, right anterior parahippocampal gyrus and left insula. Right sided extra-temporal areas of reorganization observed in patients with left hippocampal sclerosis during word encoding and bilateral lateral temporal reorganization in patients with right hippocampal sclerosis during face encoding were not associated with subsequent memory formation. Reorganization within the medial temporal lobe, however, is an efficient process. The orbitofrontal cortex is critical to subsequent memory formation in control subjects and patients. Activations within anterior cingulum and insula correlated with better verbal and visual subsequent memory in patients with left and right hippocampal sclerosis, respectively, representing effective extra-temporal recruitment.

CE verbal episodic memory impairment in schizophrenia: a comparison with frontal lobe lesion patients

Schizophrenia (SCZ)-related verbal memory impairment is hypothesized to be mediated, in part, by frontal lobe (FTL) dysfunction. However, little research has contrasted the performance of SCZ patients with that of patients exhibiting circumscribed frontal lesions. The current study compared verbal episodic memory in patients with SCZ and focal FTL lesions (left frontal, LF; right frontal, RF; and bi-frontal, BF) on a four-trial list learning task consisting of three lists of varying semantic organizational structure. Each dependent variable was examined at two levels: scores collapsed across all four trials and learning scores (i.e., trial 4-trial 1). Performance deficits were observed in each patient group across most dependent measures at both levels. Regarding patient group differences, SCZ patients outperformed LF/BF patients (i.e., either learning scores or scores collapsed across trial) on free recall, primacy, primary memory, secondary memory, and subjective organization, whereas they only outperformed RF patients on the semantically blocked list on recency and primary memory. Collectively, these results indicate that the pattern of memory performance is largely similar between patients with SCZ and those with RF lesions. These data support tentative arguments that verbal episodic memory deficits in SCZ may be mediated by frontal dysfunction in the right hemisphere.

Age-related differences in memory-encoding fMRI responses after accounting for decline in vascular reactivity

BOLD fMRI has provided a wealth of information about the aging brain. A common finding is that posterior regions of the brain manifest an age-related decrease in activation while the anterior regions show an age-related increase. Several neurocognitive models have been proposed to interpret these findings. However, one issue that has not been sufficiently considered to date is that the BOLD signal is based on vascular responses secondary to neural activity. Thus the above findings could be in part due to a vascular change, especially in view of the expected decline of vascular health with age. In the present study, we aim to examine age-related differences in memory-encoding fMRI response in the context of vascular aging. One hundred and thirty healthy subjects ranging from 20 to 89 years old underwent a scene-viewing fMRI task and, in the same session, cerebrovascular reactivity (CVR) was measured in each subject using a CO2-inhalation task. Without accounting for the influence of vascular changes, the task-activated fMRI signal showed the typical age-related decrease in visual cortex and medial temporal lobe (MTL), but manifested an increase in the right inferior frontal gyrus (IFG). In the same individuals, an age-related CVR reduction was observed in all of these regions. We then used a previously proposed normalization approach to calculate a CVR-corrected fMRI signal, which was defined as the uncorrected signal divided by CVR. Based on the CVR-corrected fMRI signal, an age-related increase is now seen in both the left and right sides of IFG; and no brain regions showed a signal decrease with age. We additionally used a model-based approach to examine the fMRI data in the context of CVR, which again suggested an age-related change in the two frontal regions, but not in the visual and MTL regions.

Parallel psychometric and cognitive modeling analyses of the Penn Face Memory Test in the Army Study to Assess Risk and Resilience in Servicemembers

OBJECTIVE

The psychometric properties of the Penn Face Memory Test (PFMT) were investigated in a large sample (4,236 participants) of U.S. Army Soldiers undergoing computerized neurocognitive testing. Data were drawn from the initial phase of the Army Study to Assess Risk and Resilience in Servicemembers (Army STARRS), a large-scale study directed towards identifying risk and resilience factors for suicidal behavior and other stress-related disorders in Army Soldiers. In this paper, we report parallel psychometric and cognitive modeling analyses of the PFMT to determine whether ability estimates derived from the measure are precise and valid indicators of memory in the Army STARRS sample.

METHOD

Single-sample cross-validation methodology combined with exploratory factor and multidimensional item response theory techniques were used to explore the latent structure of the PFMT. To help resolve rotational indeterminacy of the exploratory solution, latent constructs were aligned with parameter estimates derived from an unequal-variance signal detection model.

RESULTS

Analyses suggest that the PFMT measures two distinct latent constructs, one associated with memory strength and one associated with response bias, and that test scores are generally precise indicators of ability for the majority of Army STARRS participants.

CONCLUSIONS

These findings support the use of the PFMT as a measure of major constructs related to recognition memory and have implications for further cognitive-psychometric model development.

The Neural Correlates of Cognitive Control: Successful Remembering and Intentional Forgetting

The ability to control how we process information by remembering that which is important and forgetting that which is irrelevant is essential to maintain accurate, up-to-date memories. As such, memory success is predicated on both successful intentional encoding and successful intentional forgetting. The current study used an item-method directed forgetting paradigm to elucidate the cognitive and neural processes that underlie both processes while also examining the relationship between them to understand how the two may work together. Results indicated that encoding-related processes in the left inferior PFC and medial-temporal lobe (MTL) contribute to subsequent memory success, whereas inhibitory processes in the right superior frontal gyrus and right inferior parietal lobe contribute to subsequent forgetting success. Furthermore, connectivity analyses found a negative correlation between activity in the right superior frontal cortex and activity in the left MTL during successful intentional forgetting but not during successful encoding, incidental forgetting, or incidental encoding. Results support the theory that intentional forgetting is mediated by inhibition-related activity in the right frontal cortex and the interaction of this activity with that of encoding-related activity in the MTL. Further support for this inhibitory-related account was found through a clear dissociation between intentional and incidental forgetting, such that intentional forgetting was associated with regions shown to support inhibition, whereas incidental forgetting was associated with regions supporting encoding.

Segregating cognitive functions within hippocampal formation: a quantitative meta-analysis on spatial navigation and episodic memory

The most important cognitive domains where hippocampal formation is crucially involved are navigation and memory. Some evidence suggests that different hippocampal subregions mediate these domains. However, a quantitative meta-analysis on neuroimaging studies of spatial navigation versus memory is lacking. By means of activation likelihood estimation (ALE), we investigate concurrence of brain regions activated during spatial navigation encoding and retrieval as well as during episodic memory encoding and retrieval tasks in humans. During encoding in spatial navigation, activity was located in more posterior regions of the hippocampal formation, whereas episodic memory encoding was located in more anterior regions. Retrieval in spatial navigation was more strongly lateralized to the right compared to episodic memory retrieval. Within studies on spatial navigation retrieval, immediate recall was located more posterior and delayed recall more anterior. Overlap between concurrence of activation in spatial navigation and episodic memory was rather limited in comparison to uniquely involved regions. This argues in favor of two distinct networks, one for spatial navigation the other for episodic memory within the hippocampal formation.

Cholinergic Enhancement of Brain Activation in Mild Cognitive Impairment during Episodic Memory Encoding

OBJECTIVE

To determine the physiological impact of treatment with donepezil (Aricept) on neural circuitry supporting episodic memory encoding in patients with amnestic mild cognitive impairment (MCI) using functional magnetic resonance imaging (fMRI).

METHODS

Eighteen patients with MCI and 20 age-matched healthy controls (HC) were scanned twice while performing an event-related verbal episodic encoding task. MCI participants were scanned before treatment and after approximately 3 months on donepezil; HC were untreated but rescanned at the same interval. Voxel-level analyses assessed treatment effects on activation profiles in MCI patients relative to retest changes in non-treated HC. Changes in task-related connectivity in medial temporal circuitry were also evaluated, as were associations between brain activation, task-related functional connectivity, task performance, and clinical measures of cognition.

RESULTS

At baseline, the MCI group showed reduced activation during encoding relative to HC in the right medial temporal lobe (MTL; hippocampal/parahippocampal) and additional regions, as well as attenuated task-related deactivation, relative to rest, in a medial parietal lobe cluster. After treatment, the MCI group showed normalized MTL activation and improved parietal deactivation. These changes were associated with cognitive performance. After treatment, the MCI group also demonstrated increased task-related functional connectivity from the right MTL cluster seed region to a network of other sites including the basal nucleus/caudate and bilateral frontal lobes. Increased functional connectivity was associated with improved task performance.

CONCLUSION

Pharmacologic enhancement of cholinergic function in amnestic MCI is associated with changes in brain activation and functional connectivity during episodic memory processing which are in turn related to increased cognitive performance. fMRI is a promising biomarker for assessing treatment related changes in brain function.

The influence of attentional control on stimulus processing is category specific in Stroop tasks : Attentional control

It is still unclear how attentional control influences stimulus processing. We investigated this issue in four Stroop task experiments utilizing a pretest-training-posttest design. Subjects were given extensive training on the Stroop task using typical incongruent Stroop trials. The rates of color naming and word reading, which reflect the efficiency of stimulus processing, were assessed in pretest and posttest. The difference in rates between posttests and pretests reflects the influence of attentional control, acquired during the training phase, on stimulus processing. In Experiment 1, members of color category were used in the training phase; in Experiment 2, members of color category were used, but not in the training phase; in Experiment 3, they were neither in the color category nor were they used in the training. The results consistently showed that the suppression of word reading and the enhancement of color naming were developed in the training phases and they were not due to general training of color-naming task without conflict but to color-naming training with Stroop conflict (Experiment 4). More importantly, both suppression and enhancement affected the members of color category regardless of whether they were trained or not. The present findings suggest that the influence of attentional control on stimulus processing is category specific. We discuss the implications of the present results in terms of existing research on the locus of attentional control in Stroop tasks.

Selectivity of N170 in the left hemisphere as an electrophysiological marker for expertise in reading Chinese

OBJECTIVE

The left-lateralized N170, an event-related potential component consistently shown in response to alphabetic words, is a robust electrophysiological marker for reading expertise in an alphabetic language. In contrast, such a marker is lacking for expertise in reading Chinese, because the existing results about the lateralization of N170 for Chinese characters are mixed, reflecting complicated factors such as top-down modulation that contribute to the relative magnitudes of N170 in the left and right hemispheres. The present study aimed to explore a potential electrophysiological marker for reading expertise in Chinese with minimal top-down influence.

METHODS

We recorded N170 responses to Chinese characters and three kinds of control stimuli in a content-irrelevant task, minimizing potential top-down effects.

RESULTS

Direct comparison of the N170 amplitude in response to Chinese characters between the hemispheres showed a marginally significant left-lateralization effect. However, detailed analyses of N170 in each hemisphere revealed a more robust pattern of left-lateralization - the N170 in the left but not the right hemisphere differentiated Chinese characters from control stimuli.

CONCLUSION

These results suggest that the selectivity of N170 (a greater N170 in response to Chinese characters than to control stimuli) within the left hemisphere rather than the hemispheric difference of N170 with regard to Chinese characters is an electrophysiological marker for expertise in reading Chinese.

Localised face processing by the human prefrontal cortex: stimulation-evoked hallucinations of faces

Left and right prefrontal, premotor, and anterior temporal sites were stereotaxically implanted in order to direct surgical therapy for epilepsy. Direct electrical stimulation of the right anterior inferior frontal gyrus resulted in face-related hallucinations and illusions. When the patient was viewing a blank background, stimulation induced the experience of a rapid succession of faces. When the patient was viewing a real face, stimulation induced a series of modifications to that face. Effective stimulations induced afterdischarges that remained localised to right ventrolateral prefrontal cortex (VLPFC). Stimulation of other frontal and anterior temporal sites, bilaterally, induced no face-related hallucinations or illusions. This result supports a contribution of right VLPFC to face processing, and is consistent with models wherein it activates representations in working or declarative memories.

Lifespan development: the effects of typical aging on theory of mind

Whether typical aging is associated with impairments in social understanding is a topic of critical importance in characterizing the changes that occur in older adulthood. Theory of mind (ToM) refers to the ability to represent other's mental states, and has been tested in a variety of different paradigms in older adults. The overarching research question has been whether ToM abilities may rely on other cognitive abilities, such as processing speed or executive functioning, and as such declines in ToM may reflect a decline in general meta-representational abilities. Alternatively, ToM abilities may be relatively spared, suggesting the acquisition of a sort of social wisdom with advancing age. The preponderance of the evidence is in line with the first possibility: namely, ToM, as measured by paradigms involving faces, cartoons, stories, and videos is typically impaired in social aging, and these impairments are at least partly mediated by impairments in executive functions and fluid intelligence (but not typically by crystallized intelligence). Neuroimaging investigations suggest that older adults who perform as well as younger adults may activate compensatory mechanisms, but are impaired in the brain mechanisms most closely associated with ToM ability when their task performance is impaired. Recent methodological advances allowing continuous rather than categorical assessment of ToM show that ToM may be observed to function independently from general cognition in aging, but further investigation is needed to confirm this point. Implications of these findings for the longstanding discussion regarding Theory of Mind's endangered status as a special cognitive module are discussed.

fMRI of verbal and nonverbal memory processes in healthy and epileptogenic medial temporal lobes

Material-specific memory impairments are a well-established consequence of unilateral medial temporal lobe damage. We used fMRI to investigate encoding and recognition of verbal and nonverbal stimuli using adaptations of tasks used successfully in clinical evaluations of patients with temporal lobe epilepsy (TLE). We studied two patient groups, one with left TLE and one with right TLE, and one group of healthy subjects. Results from the healthy subjects indicated that initial and delayed recognition trials of the verbal task activated the left medial temporal lobe, and the same tasks of the nonverbal task activated the right, confirming the sensitivity to laterality of our clinical tasks. Patients tended to use the opposite hippocampus, but often the parahippocampal gyrus on the same side, compared to the healthy subjects. Since our patients and the healthy groups performed similarly on the memory tasks, we conclude that the patients' activation patterns represent an effective adaptation to the presence of an unhealthy hippocampus.

Spectral and spatial shifts of post-ictal slow waves in temporal lobe seizures

Temporal lobe seizures have a significant chance to induce impairment of normal brain functions. Even after the termination of ictal discharges, during the post-ictal period, loss of consciousness, decreased responsiveness or other cognitive dysfunctions can persist. Previous studies have found various anatomical and functional abnormalities accompanying temporal lobe seizures, including an abnormal elevation of cortical slow waves. Intracranial electroencephalography studies have shown a prominent increase of lower frequency components during and following seizures that impair (complex partial seizures) but not those that preserve (simple partial seizures) normal consciousness and responsiveness. However, due to the limited spatial coverage of intracranial electroencephalography, the investigation of cortical slow waves cannot be easily extended to the whole brain. In this study, we used scalp electroencephalography to study the spectral features and spatial distribution of post-ictal slow waves with comprehensive spatial coverage. We studied simple partial, complex partial and secondarily generalized seizures in 28 patients with temporal lobe seizures. We used dense-array electroencephalography and source imaging to reconstruct the post-ictal slow-wave distribution. In the studied cohort, we found that a 'global' spectral power shift to lower frequencies accompanied the increased severity of seizures. The delta spectral power relative to higher frequency bands was highest for secondarily generalized seizures, followed by complex partial seizures and lastly simple partial seizures. In addition to this 'global' spectral shift, we found a 'regional' spatial shift in slow-wave activity. Secondarily generalized seizures and complex partial seizures exhibited increased slow waves distributed to frontal areas with spread to contralateral temporal and parietal regions than in simple partial seizures. These results revealed that a widespread cortical network including temporal and fronto-parietal cortex is involved in abnormal slow-wave activity following temporal lobe seizures. The differential spectral and spatial shifts of post-ictal electroencephalography activity in simple partial, complex partial and secondarily generalized seizures suggest a possible connection between cortical slow waves and behavioural and cognitive changes in a human epilepsy model.

Theta power during encoding predicts subsequent-memory performance and default mode network deactivation

The subsequent memory paradigm, according to which cerebral activity for later remembered (LR) and later forgotten (LF) items is contrasted, can be used to characterize the processes necessary for successful memory encoding. Previous simultaneous electroencephalography/functional magnetic resonance imaging (EEG/fMRI) memory studies suggest an inverse relationship between frontal theta band power and the blood oxygenation level dependent (BOLD) signal in the default mode network (DMN). The principal aim of this EEG/fMRI study was to test the hypothesis that this putative theta-DMN relationship is less evident in LF compared with LR trials. Fourteen healthy participants performed an episodic memory task in which pictorial stimuli were presented during encoding, and categorized (as LR or LF) by subsequent memory performance. For each encoding trial, the mean of the Hilbert envelope of the theta signal from 400 to 800 ms after stimulus presentation was calculated. To integrate the EEG and fMRI data, general linear models (GLMs) were used to assess the extent to which these single-trial theta values (as modulators of the main effect of stimulus) predicted DMN BOLD signal change, using: (i) whole-head univariate GLMs and (ii) GLMs in which the outcome variable was the time-course of a DMN component derived from spatial independent component analysis of the fMRI data. Theta was significantly greater for LR than LF stimuli. Furthermore, the inverse relationship between theta and BOLD in the DMN was consistently stronger for LR than LF pictures. These findings imply that theta oscillations are key to attenuating processes which may otherwise impair memory encoding.

Cognitive and neural effects of semantic encoding strategy training in older adults

Prior research suggests that older adults are less likely than young adults to use effective learning strategies during intentional encoding. This functional magnetic resonance imaging (fMRI) study investigated whether training older adults to use semantic encoding strategies can increase their self-initiated use of these strategies and improve their recognition memory. The effects of training on older adults' brain activity during intentional encoding were also examined. Training increased older adults' self-initiated semantic encoding strategy use and eliminated pretraining age differences in recognition memory following intentional encoding. Training also increased older adults' brain activity in the medial superior frontal gyrus, right precentral gyrus, and left caudate during intentional encoding. In addition, older adults' training-related changes in recognition memory were strongly correlated with training-related changes in brain activity in prefrontal and left lateral temporal regions associated with semantic processing and self-initiated verbal encoding strategy use in young adults. These neuroimaging results demonstrate that semantic encoding strategy training can alter older adults' brain activity patterns during intentional encoding and suggest that young and older adults may use the same network of brain regions to support self-initiated use of verbal encoding strategies.

A preliminary study of functional abnormalities in aMCI subjects during different episodic memory tasks

Functional magnetic resonance imaging (fMRI) is an important imaging modality to understand the neurodegenerative course of mild cognitive impairment (MCI) and early Alzheimer's disease (AD), because the memory dysfunction may occur before structural degeneration is obvious. In this research, we investigated the functional abnormalities of subjects with amnestic MCI (aMCI) using three episodic memory paradigms that are relevant to different memory domains in both encoding and recognition phases. Both whole-brain analysis and region-of-interest (ROI) analysis of the medial temporal lobes (MTL), which are central to the memory formation and retrieval, were used to compare the efficiency of the different memory paradigms and the functional difference between aMCI subjects and normal control subjects. We also investigated the impact of using different functional activation measurements in ROI analysis. This pilot study could facilitate the use of fMRI activations in the MTL as a marker for early detection and monitoring progression of AD.

Effects of Δ9-Tetrahydrocannabinol Administration on Human Encoding and Recall Memory Function: A Pharmacological fMRI Study

Deficits in memory function are an incapacitating aspect of various psychiatric and neurological disorders. Animal studies have recently provided strong evidence for involvement of the endocannabinoid (eCB) system in memory function. Neuropsychological studies in humans have shown less convincing evidence but suggest that administration of cannabinoid substances affects encoding rather than recall of information. In this study, we examined the effects of perturbation of the eCB system on memory function during both encoding and recall. We performed a pharmacological MRI study with a placebo-controlled, crossover design, investigating the effects of Δ9-tetrahydrocannabinol (THC) inhalation on associative memory-related brain function in 13 healthy volunteers. Performance and brain activation during associative memory were assessed using a pictorial memory task, consisting of separate encoding and recall conditions. Administration of THC caused reductions in activity during encoding in the right insula, the right inferior frontal gyrus, and the left middle occipital gyrus and a network-wide increase in activity during recall, which was most prominent in bilateral cuneus and precuneus. THC administration did not affect task performance, but while during placebo recall activity significantly explained variance in performance, this effect disappeared after THC. These findings suggest eCB involvement in encoding of pictorial information. Increased precuneus activity could reflect impaired recall function, but the absence of THC effects on task performance suggests a compensatory mechanism. These results further emphasize the eCB system as a potential novel target for treatment of memory disorders and a promising target for development of new therapies to reduce memory deficits in humans.

Assessment of brain activity during memory encoding in a narcolepsy patient on and off modafinil using normative fMRI data

We present behavioral and functional magnetic resonance imaging (fMRI) findings of a 20-year-old female with narcolepsy who completed a standardized fMRI-adapted face memory task both 'off' and 'on' modafinil compared to a normative sample (N = 38). The patient showed poor recognition performance off modafinil (z = -2.03) but intact performance on modafinil (z = 0.78). fMRI results showed atypical activation during memory encoding off modafinil, with frontal lobe hypoactivity, but hippocampal hyperactivity, whereas all brain regions showed more normalized activation on modafinil. Results from this limited study suggest hippocampal and frontal alterations in individuals with narcolepsy. Further, the results suggest the hypothesis that modafinil may affect brain activation in some people with narcolepsy.

Reactivation of visual cortex during memory retrieval: content specificity and emotional modulation

Studies on memory retrieval suggest a reactivation of cortical regions engaged during encoding, such that visual or auditory areas reactivate for visual or auditory memories. The content specificity and any emotion dependency of such reactivations are still unclear. Because distinct visual areas are specialized in processing distinct stimulus categories, we tested for face and word specific reactivations during a memory task using functional magnetic resonance imaging (fMRI). Furthermore, because visual processing and memory are both modulated by emotion, we compared reactivation for stimuli encoded in a neutral or emotionally significant context. In the learning phase, participants studied pairs of stimuli that consisted of either a scene and a face, or a scene and a word. Scenes were either neutral or negative, but did not contain faces or words. In the test phase scenes were presented alone (one in turn), and participants indicated whether it was previously paired with a face, a word, or was new. Results from the test phase showed activation in a functionally defined face-responsive region in the right fusiform gyrus, as well as in a word-responsive region in the left inferior temporal gyrus, for scenes previously paired with faces and words, respectively. Reactivation tended to be larger in both the face- and word-responsive regions when the associated scene was negative as compared to neutral. However, relative to neutral context, the recall of faces and words paired with a negative context produced smaller activations in brain regions associated with social and semantic processing, respectively, as well as poorer memory performance overall. Taken together, these results support the idea of cortical memory reactivations, even at a content-specific level, and further suggest that emotional context may produce opposite effects on reactivations in early sensory areas and more elaborate processing in higher-level cortical areas.

Cardiorespiratory fitness, hippocampal volume, and frequency of forgetting in older adults

OBJECTIVE

The purpose of this study was to extend our earlier work to determine the extent to which cardiorespiratory fitness is associated with the frequency of memory problems via its effects on the hippocampus and spatial working memory. We hypothesized that age, sex, education, body composition, and physical activity were direct determinants of fitness, which, in turn, influenced frequency of forgetting indirectly through hippocampal volume and spatial working memory.

METHOD

We conducted assessments of demographic characteristics, Body Mass Index (BMI), physical activity, cardiorespiratory fitness, hippocampal volume, spatial working memory, and frequency of forgetting in 158 older adults (M age = 66.49). Path analyses within a covariance modeling framework were used to examine relationships among these constructs.

RESULTS

Sex, age, BMI, and education were all significant determinants of cardiorespiratory fitness. The hypothesized path models for testing the effects of fitness on frequency of forgetting through hippocampal volume and accuracy and speed of spatial working memory all fit the data well.

CONCLUSIONS

Our findings suggest that older adults with higher levels of fitness show greater preservation of hippocampal volume, which, in turn, is associated with more accurate and faster spatial memory and fewer episodes of forgetting. Given the proportion of older adults reporting memory problems, it is necessary to determine whether improvements in fitness brought about by physical activity interventions can result in subsequent attenuation of memory problems or potentially in improvements in memory.

Age-related reorganization of functional networks for successful conflict resolution: a combined functional and structural MRI study

Aging has readily observable effects on the ability to resolve conflict between competing stimulus attributes that are likely related to selective structural and functional brain changes. To identify age-related differences in neural circuits subserving conflict processing, we combined structural and functional MRI and a Stroop Match-to-Sample task involving perceptual cueing and repetition to modulate resources in healthy young and older adults. In our Stroop Match-to-Sample task, older adults handled conflict by activating a frontoparietal attention system more than young adults and engaged a visuomotor network more than young adults when processing repetitive conflict and when processing conflict following valid perceptual cueing. By contrast, young adults activated frontal regions more than older adults when processing conflict with perceptual cueing. These differential activation patterns were not correlated with regional gray matter volume despite smaller volumes in older than young adults. Given comparable performance in speed and accuracy of responding between both groups, these data suggest that successful aging is associated with functional reorganization of neural systems to accommodate functionally increasing task demands on perceptual and attentional operations.

Neural mechanisms of interference control underlie the relationship between fluid intelligence and working memory span

Fluid intelligence (gF) and working memory (WM) span predict success in demanding cognitive situations. Recent studies show that much of the variance in gF and WM span is shared, suggesting common neural mechanisms. This study provides a direct investigation of the degree to which shared variance in gF and WM span can be explained by neural mechanisms of interference control. The authors measured performance and functional magnetic resonance imaging activity in 102 participants during the n-back WM task, focusing on the selective activation effects associated with high-interference lure trials. Brain activity on these trials was correlated with gF, WM span, and task performance in core brain regions linked to WM and executive control, including bilateral dorsolateral prefrontal cortex (middle frontal gyrus; BA9) and parietal cortex (inferior parietal cortex; BA 40/7). Interference-related performance and interference-related activity accounted for a significant proportion of the shared variance in gF and WM span. Path analyses indicate that interference control activity may affect gF through a common set of processes that also influence WM span. These results suggest that individual differences in interference-control mechanisms are important for understanding the relationship between gF and WM span.

The relationship between level of processing and hippocampal-cortical functional connectivity during episodic memory formation in humans

New episodic memory traces represent a record of the ongoing neocortical processing engaged during memory formation (encoding). Thus, during encoding, deep (semantic) processing typically establishes more distinctive and retrievable memory traces than does shallow (perceptual) processing, as assessed by later episodic memory tests. By contrast, the hippocampus appears to play a processing-independent role in encoding, because hippocampal lesions impair encoding regardless of level of processing. Here, we clarified the neural relationship between processing and encoding by examining hippocampal-cortical connectivity during deep and shallow encoding. Participants studied words during functional magnetic resonance imaging and freely recalled these words after distraction. Deep study processing led to better recall than shallow study processing. For both levels of processing, successful encoding elicited activations of bilateral hippocampus and left prefrontal cortex, and increased functional connectivity between left hippocampus and bilateral medial prefrontal, cingulate and extrastriate cortices. Successful encoding during deep processing was additionally associated with increased functional connectivity between left hippocampus and bilateral ventrolateral prefrontal cortex and right temporoparietal junction. In the shallow encoding condition, on the other hand, pronounced functional connectivity increases were observed between the right hippocampus and the frontoparietal attention network activated during shallow study processing. Our results further specify how the hippocampus coordinates recording of ongoing neocortical activity into long-term memory, and begin to provide a neural explanation for the typical advantage of deep over shallow study processing for later episodic memory.

WITHDRAWN: fMRI correlates of visual working memory: What vs. where

This article has been withdrawn at the request of the authors. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy. This article has been withdrawn at the request of the editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

[Imaging in epilepsy: functional studies]

Neuroimaging studies play a fundamental role in the diagnosis and evaluation of epilepsy. Technological advances in neuroimaging techniques have made it possible to obtain functional as well as structural information. The pathophysiology of epilepsy consists of an abnormal increase in cerebral activity that can be appreciated on neuroimaging techniques like functional magnetic resonance imaging (fMRI), PET, and SPECT. In patients with epilepsy that is refractory to drug therapy, the main aim of surgery is to control seizures and thus to improve the quality of life. In the preoperative workup of these patients, fMRI has an increasingly important role, evaluating the location of functional areas that must be safeguarded during surgery.

Sex differences in the medial temporal lobe during encoding and recognition of pseudowords and abstract designs

Sex differences in various cognitive abilities have been demonstrated in terms of performance differentials and, more recently, in differences in activation patterns during fMRI. Hemispheric lateralization is sometimes accentuated in sex differences; e.g., women demonstrating greater activation of the left hemisphere than men during verbal tasks. We were interested in whether this phenomenon applies to memory for words and designs (i.e., material specific memory). Using analogous verbal (pseudowords) and nonverbal (abstract designs) encoding and recognition tasks completed back-to-back in a 3T scanner, we found that women tend to show exaggerated left hippocampal activation during certain stages of encoding and recognition of verbal information, compared with men. Likewise (although to a lesser extent), men showed more right hippocampal activation than women did during the abstract design learning task. These results have important implications for the generalization of fMRI memory study results, for example to clinical populations such as patients undergoing epilepsy surgery.

MDMA intoxication and verbal memory performance: a placebo-controlled pharmaco-MRI study

The aim of the present study was to identify the neural substrate underlying memory impairment due to a single dose of MDMA (3,4-methylenedioxymethamphetamine) by means of pharmaco-MRI. Based on previous behavioral results it was hypothesized that this deficit could be attributed to a specific influence of MDMA on encoding. Fourteen Ecstasy users participated in this double-blind, placebo-controlled, within-subject study with two treatment conditions: MDMA (75 mg) and placebo. Memory performance was tested by means of a word learning task including two words lists, one addressing reading processes (control task, CWL) and a second (experimental task, EWL) addressing encoding and reading processes. Behavioral data showed that under the influence of MDMA, EWL performance was worse than placebo. Imaging data showed that Encoding was situated mainly in (pre)frontal, temporal and parietal areas. MDMA by Encoding interaction was situated in three areas: the left middle frontal gyrus (BA10), the right fusiform gyrus (BA19), and the left cuneus (BA18). Behavioral and functional data only correlated in BA10. It appeared that EWL performance caused BOLD signal change in BA10 during placebo treatment but not during MDMA intoxication. It is concluded that MDMA influences middle frontal gyrus processes resulting in impoverished memory encoding.

Preoperative prediction of verbal episodic memory outcome using FMRI

This article focuses on an important neurosurgical problem for which functional imaging may have a role. Temporal lobe epilepsy surgery typically involves removal of much of the anterior medial temporal lobe, which is critical for encoding and retrieval of long-term episodic memories. Verbal episodic memory decline after left anterior temporal lobe resection occurs in 30% to 60% of such patients. Recent studies show that preoperative fMRI can predict the degree of verbal memory change that will occur, and that fMRI improves prediction accuracy when combined with other routine tests. The predictive power of fMRI appears to be at least as good as the Wada memory test, making fMRI a viable noninvasive alternative to the Wada for preoperative assessment.

Bilateral hippocampal dysfunction in schizophrenia

The hippocampus has long been known to be important for memory, with the right hippocampus particularly implicated in nonverbal/visuo-spatial memory and the left in verbal/narrative or episodic memory. Despite this hypothesized lateralized functional difference, there has not been a single task that has been shown to activate both the right and left hippocampi differentially, dissociating the two, using neuroimaging. The transverse patterning (TP) task is a strong candidate for this purpose, as it has been shown in human and nonhuman animal studies to theoretically and empirically depend on the hippocampus. In TP, participants choose between stimuli presented in pairs, with the correct choice being a function of the specific pairing. In this project, TP was used to assess lateralized hippocampal function by varying its dependence on verbal material, with the goal of dissociating the two hippocampi. Magnetoencephalographic (MEG) data were collected while controls performed verbal and nonverbal versions of TP in order to verify and validate lateralized activation within the hippocampi. Schizophrenia patients were evaluated to determine whether they exhibited a lateralized hippocampal deficit. As hypothesized, patients' mean level of behavioral performance was poorer than controls' on both verbal and nonverbal TP. In contrast, patients had no decrement in performance on a verbal and nonverbal non-hippocampal-dependent matched control task. Also, controls but not patients showed more right hippocampal activation during nonverbal TP and more left hippocampal activation during verbal TP. These data demonstrate the capacity to assess lateralized hippocampal function and suggest a bilateral hippocampal behavioral and activation deficit in schizophrenia.

Cognitive control and right ventrolateral prefrontal cortex: reflexive reorienting, motor inhibition, and action updating

Delineating the functional organization of the prefrontal cortex is central to advancing models of goal-directed cognition. Considerable evidence indicates that specific forms of cognitive control are associated with distinct subregions of the left ventrolateral prefrontal cortex (VLPFC), but less is known about functional specialization within the right VLPFC. We report a functional MRI meta-analysis of two prominent theories of right VLPFC function: stopping of motor responses and reflexive orienting to abrupt perceptual onsets. Along with a broader review of right VLPFC function, extant data indicate that stopping and reflexive orienting similarly recruit the inferior frontal junction (IFJ), suggesting that IFJ supports the detection of behaviorally relevant stimuli. By contrast, other right VLPFC subregions are consistently active during motor inhibition, but not reflexive reorienting tasks, with posterior-VLPFC being active during the updating of action plans and mid-VLPFC responding to decision uncertainty. These results highlight the rich functional heterogeneity that exists within right VLPFC.

Visual personal familiarity in amnestic mild cognitive impairment

BACKGROUND

Patients with amnestic mild cognitive impairment are at high risk for developing Alzheimer's disease. Besides episodic memory dysfunction they show deficits in accessing contextual knowledge that further specifies a general concept or helps to identify an object or a person.

METHODOLOGY/PRINCIPAL FINDINGS

Using functional magnetic resonance imaging, we investigated the neural networks associated with the perception of personal familiar faces and places in patients with amnestic mild cognitive impairment and healthy control subjects. Irrespective of stimulus type, patients compared to control subjects showed lower activity in right prefrontal brain regions when perceiving personally familiar versus unfamiliar faces and places. Both groups did not show different neural activity when perceiving faces or places irrespective of familiarity.

CONCLUSIONS/SIGNIFICANCE

Our data highlight changes in a frontal cortical network associated with knowledge-based personal familiarity among patients with amnestic mild cognitive impairment. These changes could contribute to deficits in social cognition and may reduce the patients' ability to transition from basic to complex situations and tasks.

Individual differences in neural activity during a facial expression vs. identity working memory task

Facial expressions of emotion constitute a critical portion of our non-verbal social interactions. In addition, the identity of the individual displaying this expression is critical to these interactions as they embody the context in which these expressions will be interpreted. To identify any overlapping and/or unique brain circuitry involved in the processing of these two information streams in a laboratory setting, participants performed a working memory (WM) task (i.e., n-back) in which they were instructed to monitor either the expression (EMO) or the identity (ID) of the same set of face stimuli. Consistent with previous work, during both the EMO and ID tasks, we found a significant increase in activity in dorsolateral prefrontal cortex (DLPFC) supporting its generalized role in WM. Further, individuals that showed greater DLPFC activity during both tasks also showed increased amygdala activity during the EMO task and increased lateral fusiform gyrus activity during the ID task. Importantly, the level of activity in these regions significantly correlated with performance on the respective tasks. These findings provide support for two separate neural circuitries, both involving the DLPFC, supporting working memory for the faces and expressions of others.

Semantic congruence enhances memory of episodic associations: role of theta oscillations

Growing evidence suggests that theta oscillations play a crucial role in episodic encoding. The present study evaluates whether changes in electroencephalographic theta source dynamics mediate the positive influence of semantic congruence on incidental associative learning. Here we show that memory for episodic associations (face-location) is more accurate when studied under semantically congruent contexts. However, only participants showing RT priming effect in a conceptual priming test (priming group) also gave faster responses when recollecting source information of semantically congruent faces as compared with semantically incongruent faces. This improved episodic retrieval was positively correlated with increases in theta power during the study phase mainly in the bilateral parahippocampal gyrus, left superior temporal gyrus, and left lateral posterior parietal lobe. Reconstructed signals from the estimated sources showed higher theta power for congruent than incongruent faces and also for the priming than the nonpriming group. These results are in agreement with the attention to memory model. Besides directing top-down attention to goal-relevant semantic information during encoding, the dorsal parietal lobe may also be involved in redirecting attention to bottom-up-driven memories thanks to connections between the medial-temporal and the left ventral parietal lobe. The latter function can either facilitate or interfere with encoding of face-location associations depending on whether they are preceded by semantically congruent or incongruent contexts, respectively, because only in the former condition retrieved representations related to the cue and the face are both coherent with the person identity and are both associated with the same location.

Developmental fMRI study of episodic verbal memory encoding in children

BACKGROUND

Understanding the maturation and organization of cognitive function in the brain is a central objective of both child neurology and developmental cognitive neuroscience. This study focuses on episodic memory encoding of verbal information by children, a cognitive domain not previously studied using fMRI.

METHODS

Children from 7 to 19 years of age were scanned at 1.5-T field strength using event-related fMRI while performing a novel verbal memory encoding paradigm in which words were incidentally encoded. A subsequent memory analysis was performed. SPM2 was utilized for whole brain and region-of-interest analyses of data. Both whole-sample intragroup analyses and intergroup analyses of the sample divided into 2 subgroups by age were conducted.

RESULTS

Importantly, behavioral memory performance was equal across the age range of children studied. Encoding-related activation in the left hippocampus and bilateral basal ganglia declined as age increased. In addition, while robust blood oxygen level-dependent signal was found in left prefrontal cortex with task performance, no encoding-related age-modulated prefrontal activation was observed in either hemisphere.

CONCLUSION

These data are consistent with a developmental pattern of verbal memory encoding function in which left hippocampal and bilateral basal ganglionic activations are more robust earlier in childhood but then decline with age. No encoding-related activation was found in prefrontal cortex which may relate to this region's recognized delay in biologic maturation in humans. These data represent the first fMRI demonstration of verbal encoding function in children and are relevant developmentally and clinically.