FDG-PET analysis and findings in amnesia resulting from hypoxia

Retrograde amnesia abolishes the self-reference effect in anterograde memory

Is retrograde amnesia associated with an ability to know who we are and imagine what we will be like in the future? To answer this question, we had S.G., a patient with focal retrograde amnesia following hypoxia, two brain-damaged (control) patients with no retrograde memory deficits, and healthy controls judge whether each of a series of trait adjectives was descriptive of their present self, future self, another person, and that person in the future, and later recognize studied traits among distractors. Healthy controls and control patients were more accurate in recognizing self-related compared to other-related traits, a phenomenon known as the self-reference effect (SRE). This held for both present and future self-views. By contrast, no evidence of (present or future) SRE was observed in SG, who concomitantly showed reduced certainty about his personality traits. These findings indicate that retrograde amnesia can weaken the self-schema and preclude its instantiation during self-related processing.

Increased Pupil Size during Future Thinking in a Subject with Retrograde Amnesia

Recent research has assessed pupil size during past thinking in patients with retrograde amnesia. Building on this research, we assessed pupil size during future thinking in a retrograde amnesia patient. To this end, we measured pupil size during past and future thinking in L, a 19-year-old, right-handed man free of neurological/psychiatric disorders except for retrograde amnesia that occurred after an episode of fugue. During a past thinking condition, we invited L to retrieve retrograde events (i.e., events that occurred before amnesia) and anterograde events (i.e., events that occurred after amnesia). During a future thinking condition, we invited him to imagine events that might occur the following week, the following month, and in the new year. Past and future thinking occurred while L's pupil size was monitored with eye-tracking glasses. L demonstrated higher specificity during future than during past thinking. Critically, the results demonstrated a larger pupil size during future than during past thinking. The larger pupil size during future thinking observed in L can be attributed to the high cognitive load involved in future thinking. Our study not only demonstrates preserved future thinking in a patient with dissociative retrograde amnesia, but also shows that pupillometry can be used for the physiological assessment of future thinking in retrograde amnesia patients.

Long-term cognitive and psychiatric outcomes of acute respiratory distress syndrome managed with Extracorporeal Membrane Oxygenation

BACKGROUND

Cognitive dysfunction is often reported in patients who have experienced acute respiratory distress syndrome (ARDS). Extra Corporeal Membrane Oxygenation (ECMO) therapy is increasingly used to manage ARDS patients in ICU, transforming survival rates. However, few studies have examined cognitive outcomes.

METHODS

We examined self-reported cognitive complaints, psychiatric outcomes and neuropsychological test performance in survivors of severe hypoxaemia managed with VV-ECMO, at 18-24 month follow-up, compared with a group of healthy controls.

RESULTS

Over 70% of ECMO-treated patients (N = 46) complained of difficulty in at least one aspect of cognition on self-report measures (study 1). However, a much lower frequency of cognitive impairment was found on formal neuropsychological testing (study 2). Mean neuropsychological test scores of the ECMO group (N = 24) did not significantly differ from healthy controls (N = 23) after controlling for depression. Less than 30% of ECMO-treated patients showed impairments in anterograde memory, and deficits on general IQ or executive function were seen in <17% of patients. However, we observed high levels of self-reported anxiety and depression in the ECMO-treated patients.

CONCLUSIONS

Cognitive outcomes in ECMO-treated patients were generally good, with preserved neuropsychological function in the majority of patients, despite severe hypoxaemia and high rates of self-reported difficulties. However, we saw high levels of mental health symptoms in these patients, highlighting a need for psychological support.

Amnesia in your pupils: decreased pupil size during autobiographical retrieval in a case of retrograde amnesia

We investigate whether retrograde-amnesia can be indexed with pupil activity. We present the case of L, 19-year-old, without neurological or psychiatric disorders except for retrograde-amnesia. We invited L to retrieve retrograde and anterograde memories while his pupil size was monitering with eye-tracking glasses. Results demonstrated impaired retrograde retrieval but successful anterograde retrieval in L. He also attributed lower emotional value and visual imagery to his retrograde compared to his anterograde memories. Critically, smaller pupils were observed during retrograde than during anterograde retrieval. Our study provides the first evidence on the value of pupillometry as a potential physiological marker of amnesia.

Network-wide abnormalities explain memory variability in hippocampal amnesia

Patients with hippocampal amnesia play a central role in memory neuroscience but the neural underpinnings of amnesia are hotly debated. We hypothesized that focal hippocampal damage is associated with changes across the extended hippocampal system and that these, rather than hippocampal atrophy per se, would explain variability in memory between patients. We assessed this hypothesis in a uniquely large cohort of patients (n = 38) after autoimmune limbic encephalitis, a syndrome associated with focal structural hippocampal pathology. These patients showed impaired recall, recognition and maintenance of new information, and remote autobiographical amnesia. Besides hippocampal atrophy, we observed correlatively reduced thalamic and entorhinal cortical volume, resting-state inter-hippocampal connectivity and activity in posteromedial cortex. Associations of hippocampal volume with recall, recognition, and remote memory were fully mediated by wider network abnormalities, and were only direct in forgetting. Network abnormalities may explain the variability across studies of amnesia and speak to debates in memory neuroscience.

Neuropsychological Investigations of Human Amnesia: Insights Into the Role of the Medial Temporal Lobes in Cognition

The past 30 years of research on human amnesia has yielded important changes in our understanding of the role of the medial temporal lobes (MTL) in memory. On the one hand, this body of evidence has highlighted that not all types of memory are impaired in patients with MTL lesions. On the other hand, this research has made apparent that the role of the MTL extends beyond the domain of long-term memory, to include working memory, perception, and future thinking. In this article, we review the discoveries and controversies that have characterized this literature and that set the stage for a new conceptualization of the role of the MTL in cognition. This shift toward a more nuanced understanding of MTL function has direct relevance for a range of clinical disorders in which the MTL is implicated, potentially shaping not only theoretical understanding but also clinical practice. (JINS, 2017, 23, 732-740).

Hippocampal and diencephalic pathology in developmental amnesia

Developmental amnesia (DA) is a selective episodic memory disorder associated with hypoxia-induced bilateral hippocampal atrophy of early onset. Despite the systemic impact of hypoxia-ischaemia, the resulting brain damage was previously reported to be largely limited to the hippocampus. However, the thalamus and the mammillary bodies are parts of the hippocampal-diencephalic network and are therefore also at risk of injury following hypoxic-ischaemic events. Here, we report a neuroimaging investigation of diencephalic damage in a group of 18 patients with DA (age range 11-35 years), and an equal number of controls. Importantly, we uncovered a marked degree of atrophy in the mammillary bodies in two thirds of our patients. In addition, as a group, patients had mildly reduced thalamic volumes. The size of the anterior-mid thalamic (AMT) segment was correlated with patients' visual memory performance. Thus, in addition to the hippocampus, the diencephalic structures also appear to play a role in the patients' memory deficit.

A Special Extract of Bacopa monnieri (CDRI-08)-Restored Memory in CoCl2-Hypoxia Mimetic Mice Is Associated with Upregulation of Fmr-1 Gene Expression in Hippocampus

Fragile X mental retardation protein (FMRP) is a neuronal translational repressor and has been implicated in learning, memory, and cognition. However, the role of Bacopa monnieri extract (CDRI-08) in enhancing cognitive abilities in hypoxia-induced memory impairment via Fmr-1 gene expression is not known. Here, we have studied effects of CDRI-08 on the expression of Fmr-1 gene in the hippocampus of well validated cobalt chloride (CoCl2)-induced hypoxia mimetic mice and analyzed the data with alterations in spatial memory. Results obtained from Morris water maze test suggest that CoCl2 treatment causes severe loss of spatial memory and CDRI-08 is capable of reversing it towards that in the normal control mice. Our semiquantitative RT-PCR, Western blot, and immunofluorescence microscopic data reveal that CoCl2-induced hypoxia significantly upregulates the expression of Hif-1α and downregulates the Fmr-1 expression in the hippocampus, respectively. Further, CDRI-08 administration reverses the memory loss and this is correlated with significant downregulation of Hif-1α and upregulation of Fmr-1 expression. Our data are novel and may provide mechanisms of hypoxia-induced impairments in the spatial memory and action of CDRI-08 in the recovery of hypoxia led memory impairment involving Fmr-1 gene encoded protein called FMRP.

Focal retrograde amnesia and the attribution of causality: An exceptionally critical view

A detailed critique of the literature on focal retrograde amnesia is provided. Some of the cases commonly cited in this literature had, in fact, severely impaired anterograde memory, most often involving visuospatial material. Other cases showed poor anterograde memory in more moderate or subtle form, begging the question of whether "like" had really been compared with "like" across the retrograde and anterograde domains: there may be alternative explanations for the observed patterns of performance. One suggestion is that these patients suffer an impairment of long-term consolidation, an attractive hypothesis but one which requires much more rigorous testing than has occurred to date and which implies that the underlying problem is not specific to retrograde memory. Moreover, within the literature on cases of focal retrograde amnesia, differing patterns of performance on tests of autobiographical memory or remote semantic knowledge have been reported, and sometimes these may have reflected factors other than the sites of lesions. Many of the most convincing cases in this literature have been those in whom there was an initially severe anterograde amnesia as well as an extensive retrograde loss: in these cases, the critical issue is what determines differential patterns of recovery across these domains-it is likely that both physiological and psychological factors are important. A second, somewhat different, group are patients with semantic dementia, who show a pronounced recency effect in remote memory but, in these cases, the most parsimonious explanation may be in terms of predominantly semantic/linguistic and/or strategic factors. A third group are those with transient epileptic amnesia but, in these cases, the memory gaps may reflect past (anterograde) ictal activity. A fourth group are those in whom psychogenic factors may well be relevant. Although it is difficult to "prove" psychological causation, the logical difficulties in attributing causation where brain lesions are either very subtle or multiple have been considerably underestimated in the neuropsychological literature. Given these problems, in uncertain or equivocal cases, it is as critical to present the relevant psychological data for the reader to evaluate as it is to provide the pertinent memory test scores: this is underemphasised in many of the studies reviewed. Publication of cases in the absence of such data may lead to faulty clinical, neuropsychological, and cognitive conclusions. Abbreviations : AA: anterograde amnesia; AMI: Autobiographical Memory Interview; PTA: posttraumatic amnesia; RA: retrograde amnesia; RMT: Recognition Memory Test; TEA: transient epileptic amnesia; TGA: transient global amnesia; WMS: Wechsler Memory Scale.

Transient gastric irritation in the neonatal rats leads to changes in hypothalamic CRF expression, depression- and anxiety-like behavior as adults

AIMS

A disturbance of the brain-gut axis is a prominent feature in functional bowel disorders (such as irritable bowel syndrome and functional dyspepsia) and psychological abnormalities are often implicated in their pathogenesis. We hypothesized that psychological morbidity in these conditions may result from gastrointestinal problems, rather than causing them.

METHODS

Functional dyspepsia was induced by neonatal gastric irritation in male rats. 10-day old male Sprague-Dawley rats received 0.1% iodoacetamide (IA) or vehicle by oral gavage for 6 days. At 8-10 weeks of age, rats were tested with sucrose preference and forced-swimming tests to examine depression-like behavior. Elevated plus maze, open field and light-dark box tests were used to test anxiety-like behaviors. ACTH and corticosterone responses to a minor stressor, saline injection, and hypothalamic CRF expression were also measured.

RESULTS

Behavioral tests revealed changes of anxiety- and depression-like behaviors in IA-treated, but not control rats. As compared with controls, hypothalamic and amygdaloid CRF immunoreactivity, basal levels of plasma corticosterone and stress-induced ACTH were significantly higher in IA-treated rats. Gastric sensory ablation with resiniferatoxin had no effect on behaviors but treatment with CRF type 1 receptor antagonist, antalarmin, reversed the depression-like behavior in IA-treated rats

CONCLUSIONS

The present results suggest that transient gastric irritation in the neonatal period can induce a long lasting increase in depression- and anxiety-like behaviors, increased expression of CRF in the hypothalamus, and an increased sensitivity of HPA axis to stress. The depression-like behavior may be mediated by the CRF1 receptor. These findings have significant implications for the pathogenesis of psychological co-morbidity in patients with functional bowel disorders.

Selective lamina dysregulation in granular retrosplenial cortex (area 29) after anterior thalamic lesions: an in situ hybridization and trans-neuronal tracing study in rats

There is growing evidence that lesions of the anterior thalamic nuclei cause long-lasting intrinsic changes to retrosplenial cortex, with the potential to alter its functional properties. The present study had two goals. The first was to identify the pattern of changes in eight markers, as measured by in-situ hydridisation, in the granular retrosplenial cortex (area Rgb) following anterior thalamic lesions. The second was to use retrograde trans-neuronal tracing methods to identify the potential repercussions of intrinsic changes within granular retrosplenial cortex. In Experiment 1, adult rats received unilateral lesions of the anterior thalamic nuclei and were perfused 4 weeks later. Of the eight markers, four (c-fos, zif268, 5ht2rc, kcnab2) showed a very similar pattern of change, with decreased levels in superficial retrosplenial cortex (lamina II) in the ipsilateral hemisphere but little or no change in deeper layers (lamina V). A fifth marker (cox6b) showed a shift in activity levels in the opposite direction to the previous four markers. Three other markers (cox6a1, CD74, ncs-1) did not appear to change activity levels after surgery. The predominant pattern of change, a decrease in superficial cortical activity, points to potential alterations in plasticity and metabolism. In Experiment 2, wheat germ agglutin (WGA) was injected into the anterior thalamic nuclei in rats given different survival times, sometimes in combination with the retrograde, fluorescent tracer, Fast Blue. Dense aggregations of retrogradely labeled cells were always found in lamina VI of granular retrosplenial cortex, but additional labeled cells in lamina II were only found: (1) in WGA cases, that is never after Fast Blue injections, and (2) after longer WGA survival times (3 days). These layer II Rgb cells are likely to have been trans-neuronally labeled, revealing a pathway from lamina II of Rgb to those deeper retrosplenial cells that project directly to the anterior thalamic nuclei.

High altitude memory impairment is due to neuronal apoptosis in hippocampus, cortex and striatum

Cognitive and neuropsychological functions have been impaired at high altitude and the effects depend on altitude and duration of stay. However, the neurobiological mechanism of this impairment is poorly understood especially exposure to different duration. Aim of the present study was to investigate the changes of behavior, biochemistry and morphology after exposure to different duration of hypobaric hypoxia. The rats were exposed continuously to a simulated high altitude of 6100m for 3, 7, 14 and 21 days in an animal decompression chamber. Spatial reference memory was tested by Morris water maze. The oxidative stress markers like free radicals, NO, lipid peroxidation, LDH activity and antioxidant systems like GSH, GSSG, GPx, GR, SOD were estimated from cortex, hippocampus and striatum. The morphological changes, neurodegeneration, DNA fragmentation and mode of cell death have also been studied. It was observed that the spatial reference memory was significantly affected after exposure to hypobaric hypoxia. Increased oxidative stress markers along with decreased effectiveness of antioxidant system were also observed in hypoxia-exposed animals. Further pyknotic, shrunken, tangle-like neurons were observed in all these regions after hypoxia and neurodegeneration, DNA fragmentation and apoptosis were also observed in all the three regions. But after 21 days of exposure, the spatial memory was improved along with improvement of antioxidant activities. Our result suggests that the apoptotic death may be involved in HA-induced memory impairment and after 7 days of exposure the effect was more pronounced but after 21 days of exposure recovery was observed.

Anterior thalamic lesions produce chronic and profuse transcriptional de-regulation in retrosplenial cortex: A model of retrosplenial hypoactivity and covert pathology

Anterior thalamic lesions are thought to produce 'covert pathology' in retrosplenial cortex, but the causes are unknown. Microarray analyses tested the hypothesis that thalamic damage causes a chronic, hypo-function of metabolic and plasticity-related pathways (Experiment 1). Rats with unilateral, anterior thalamic lesions were exposed to a novel environment for 20 minutes, and granular retrosplenial tissue sampled from both hemispheres 30 minutes, 2h, or 8h later. Complementary statistical approaches (analyses of variance, predictive patterning and gene set enrichment analysis) revealed pervasive gene expression differences between retrosplenial cortex ipsilateral to the thalamic lesion and contralateral to the lesion. Selected gene differences were validated by QPCR, immunohistochemistry (Experiment 1), and in situ hybridisation (Experiment 2). Following thalamic lesions, the retrosplenial cortex undergoes profuse cellular transcriptome changes including lower relative levels of specific mRNAs involved in energy metabolism and neuronal plasticity. These changes in functional gene expression may be largely driven by decreases in the expression of multiple transcription factors, including brd8, c-fos, fra-2, klf5, nfix, nr4a1, smad3, smarcc2, and zfp9, with a much smaller number (nfat5, neuroD1, RXRγ) showing increases. These findings have implications for conditions such as diencephalic amnesia and Alzheimer's disease, where both anterior thalamic pathology and retrosplenial cortex hypometabolism are prominent.

The role of imaging in United States courtrooms

The rapid evolution of brain imaging techniques has increasingly offered more detailed diagnostic and prognostic information about neurologic and psychiatric disorders and the structural and functional brain changes that may influence behavior. Coupled with these developments is the increasing use of neuroimages in courtrooms, where they are used as evidence in criminal cases to challenge a defendant's competency or culpability and in civil cases to establish physical injury or toxic exposure. Several controversies exist, including the admissibility of neuroimages in legal proceedings, the reliability of expert testimony, and the appropriateness of drawing conclusions in individual cases based on the findings of research uses of imaging technology. This article reviews and discusses the current state of these issues.

Lance-Adams syndrome: a report of two cases

Chronic post-hypoxic myoclonus, also known as Lance-Adams syndrome (LAS), is a rare complication of successful cardiopulmanry resuscitation often accompanied by action myoclonus and cerebellar ataxia. It is seen in patients who have undergone a cardiorespiratory arrest, regained consciousness afterwards, and then developed myoclonus days or weeks after the event. Worldwide, 122 cases have been reported in the literature so far, including 1 case of Chinese. Here we report 2 Chinese LAS patients with detailed neuroimagings. Cranial single photon emission computed tomography (SPECT) of patient 1, a 52-year-old woman, showed a mild hypoperfusion in her left temporal lobe, whereas patient 2, a 54-year-old woman, manifested a mild bilateral decrease of glucose metabolism in the frontal lobes and a mild to moderate decrease of the N-acetyl aspartate (NAA) peak in the bilateral hippocampi by cranial [(18)F]-fluorodeoxyglucose positron emission tomographic (PET) scan and cranial magnetic resonance spectroscopy (MRS), respectively. We also review the literature on the neuroimaging, pathogenesis, and treatment of LAS.

Prognostic value of posteromedial cortex deactivation in mild cognitive impairment

BACKGROUND

Normal subjects deactivate specific brain regions, notably the posteromedial cortex (PMC), during many tasks. Recent cross-sectional functional magnetic resonance imaging (fMRI) data suggests that deactivation during memory tasks is impaired in Alzheimer's disease (AD). The goal of this study was to prospectively determine the prognostic significance of PMC deactivation in mild cognitive impairment (MCI).

METHODOLOGY/PRINCIPAL FINDINGS

75 subjects (34 MCI, 13 AD subjects and 28 controls) underwent baseline fMRI scanning during encoding of novel and familiar face-name pairs. MCI subjects were followed longitudinally to determine conversion to AD. Regression and analysis of covariance models were used to assess the effect of PMC activation/deactivation on conversion to dementia as well as in the longitudinal change in dementia measures. At longitudinal follow up of up to 3.5 years (mean 2.5+/-0.79 years), 11 MCI subjects converted to AD. The proportion of deactivators was significantly different across all groups: controls (79%), MCI-Nonconverters (73%), MCI-converters (45%), and AD (23%) (p<0.05). Mean PMC activation magnitude parameter estimates, at baseline, were negative in the control (-0.57+/-0.12) and MCI-Nonconverter (-0.33+/-0.14) groups, and positive in the MCI-Converter (0.37+/-0.40) and AD (0.92+/-0.30) groups. The effect of diagnosis on PMC deactivation remained significant after adjusting for age, education and baseline Mini-Mental State Exam (p<0.05). Baseline PMC activation magnitude was correlated with change in dementia ratings from baseline.

CONCLUSION

Loss of physiological functional deactivation in the PMC may have prognostic value in preclinical AD, and could aid in profiling subgroups of MCI subjects at greatest risk for progressive cognitive decline.

Cortical deactivation in mild cognitive impairment: high-field-strength functional MR imaging

PURPOSE

To prospectively identify brain regions in which task-related changes in activation during a memory encoding task, measured with functional magnetic resonance (MR) imaging, correlate with degree of memory impairment across Alzheimer disease (AD), mild cognitive impairment (MCI), and elderly control subjects.

MATERIALS AND METHODS

The institutional review board approved this HIPAA-compliant study, and each patient gave written informed consent. Seventy-five subjects (mean age, 72.9 years+/-7.2 [standard deviation]; 37 men, 38 women)-13 patients with mild AD, 34 individuals with amnestic MCI, and 28 healthy elderly control subjects-were imaged at 4.0 T during novel encoding (NE) and familiar encoding (FE) of face-name pairs presented within a block design for later retrieval. Blood oxygen level-dependent (BOLD) changes were assessed across the entire brain for each group. Between-subject analysis identified brain regions demonstrating a monotonic increase or decrease in activation magnitude, from control subjects to patients with MCI to patients with mild AD. BOLD response was also correlated with score on the delayed portion of the California Verbal Learning Test (CVLT).

RESULTS

In controls, the task elicited positive activation (NE>FE) in the dorsolateral prefrontal, lateral parietal, and medial temporal regions, and negative activation (FE>NE) in the midline frontal and parietal regions. Along the spectrum from control subjects to patients with AD, there was decreasing activation in the medial temporal lobe (MTL), including the hippocampus and parahippocampal and fusiform gyri, and increasing activation in the posteromedial cortices (PMCs), primarily in the precuneus and posterior cingulate gyrus. Activation magnitude in the PMCs significantly (P<.001, r=-0.502) correlated with CVLT score.

CONCLUSION

Compared with activation in the MTL, deactivation in the PMCs could be a more sensitive marker of early AD at functional MR imaging.

Hypobaric hypoxia-induced dendritic atrophy of hippocampal neurons is associated with cognitive impairment in adult rats

Simulated hypobaric hypoxia (HBH), resembling high altitude hypoxia severely affects the CNS and results in several physiological changes. The hippocampus is closely associated with learning and memory and an insult to this region affects cognition. Previous studies suggest that rapid or prolonged exposures to HBH are associated with psychomotor and cognitive impairments. The defense personnel, mountain climbers and rescue teams are exposed to such harsh environment and thus it demands a systematic study emphasizing the subtle effects of such extreme environments on cognitive function. Accordingly, this study evaluated the effect of hypobaric hypoxia on structural changes in the principal neurons of the hippocampus and learning in eight-arm radial maze. Adult male Wistar rats, subjected to simulated hypobaric hypoxia equivalent to an altitude of 6000 m for a period of 2 or 7 days, in a hypoxic chamber served as hypoxic group (HY). Rats housed in a similar chamber for the same period of time, without hypoxic exposure served as sham control (SC), while normal control (NC) group of rats were housed in standard laboratory conditions. The dendritic morphology of neurons in cornu ammonis region 1 (CA1) and cornu ammonis region 3 (CA3) was studied in Golgi-impregnated hippocampal sections. Exposure for 2 days to hypobaric hypoxia had minimal deleterious effects on the CA1 pyramidal neurons, while exposure for 7 days resulted in a significant decrease in the number of branching points, intersections and dendritic length. Unlike the CA1 pyramidal neurons, the CA3 neurons exhibited dendritic atrophy following both 2 and 7 days of hypoxic exposure. Further, hippocampal-dependent spatial learning was affected marginally following 2 day exposure, while 7 day exposure severely affected learning of the partially baited radial arm maze task. Our study suggests that dendritic atrophy in the hippocampus on exposure to HBH could be one of the bases for the cognitive deficits exhibited under such conditions.

Electrophysiological correlates of deficient encoding in a case of post-anoxic amnesia

Little is known about the initial stages of information processing in amnesia as compared to normal memory. In this study, we used electrical spatiotemporal mapping to compare cortical activation during encoding and recognition in a 56-year-old patient with severe, chronic post-anoxic amnesia and an age-matched control group. Event-related potentials were recorded as the subjects performed a continuous recognition task composed of meaningful designs. Activation in the control group rapidly progressed through eight different electrocortical configurations over 700 ms after onset of new stimuli. In contrast, activation in the amnesic patient was highly monotonous: it showed varying electrocortical patterns only during the first 150 ms but then remained abnormally stable for the remainder of the analysed time window. Electrical source localisation revealed that the patient failed to activate distributed cortical networks and that his processing was confined to visual areas. The present study suggests that the rapid activation of distributed cortical networks is critical for efficient encoding.

Recall and recognition memory in amnesia: patients with hippocampal, medial temporal, temporal lobe or frontal pathology

The relationship between recall and recognition memory impairments was examined in memory-disordered patients with either hippocampal, medial temporal, more widespread temporal lobe or frontal pathology. The Hirst [Hirst, W., Johnson, M. K., Phelps, E. A., & Volpe, B. T. (1988). More on recognition and recall in amnesics. Journal of Experimental Psychology: Learning, Memory, & Cognition, 14, 758-762] technique for titrating exposure times was used to match recognition memory performance as closely as possible before comparing recall memory scores. Data were available from two different control groups given differing exposure times. Each of the patient groups showed poorer recall memory performance than recognition scores, proportionate to the difference seen in healthy participants. When patients' scores were converted to Z-scores, there was no significant difference between mean Z-recall and Z-recognition scores. When plotted on a scatterplot, the majority of the data-points indicating disproportionately low recall memory scores came from healthy controls or patients with pathology extending into the lateral temporal lobes, rather than from patients with pathology confined to the medial temporal lobes. Patients with atrophy extending into the parahippocampal gyrus (H+) performed worse than patients with atrophy confined to the hippocampi (H-); but, when H- patients were given a shorter exposure time (5s) and compared with H+ at a longer exposure (10s), their performance was virtually identical and did not indicate any disproportionate recall memory impairment in the H- group. Parahippocampal volumes on MRI correlated significantly with both recall and recognition memory. The possibility that findings were confounded by inter-stimulus artefacts was examined and rejected. These findings argue against the view that hippocampal amnesia or memory disorders in general are typically characterised by a disproportionate impairment in recall memory. Disproportionate recall memory impairment has been observed in a number of published cases, and the reason for the varying pattern obtained across hippocampal patients requires further examination.

Correlations of regional cerebral metabolism with memory performance and executive function in patients with herpes encephalitis or frontal lobe lesions

Cerebral [18F]fluorodeoxyglucose positron emission tomography (18FDG-PET) data from patients suffering amnesia following herpes encephalitis (n=7) or frontal lobe pathology (n=14) were compared with data from age-matched nonamnesic subjects (n=10). All subjects received structural MRI, resting 18FDG-PET scans, and neuropsychological evaluation. PET data were analyzed using complementary statistical parametric mapping and region-of-interest methods. Differential patterns of hypometabolism were found in patients relative to healthy controls. Factor analysis of the neuropsychological data revealed that memory performance was associated with retrosplenial and medial temporal metabolism, and executive function was associated with dorsolateral frontal metabolism. The association between memory performance and retrosplenial metabolism remained statistically significant after accounting for measures of cerebral atrophy using MRI. The significance of the retrosplenium as a major relay station between the thalamus and the medial temporal and frontal lobes--sensitive to changes in either--is discussed in the light of the findings.

Functional-anatomic correlates of memory retrieval that suggest nontraditional processing roles for multiple distinct regions within posterior parietal cortex

Current theories of posterior parietal cortex (PPC) function emphasize space-based attention and motor intention. Imaging studies of long-term memory have demonstrated PPC activation during successful memory retrieval. Here, we explored the relationship between memory processes and classical notions of PPC function. Study 1 investigated old-new recognition using picture and sound stimuli to test whether PPC memory effects were dependent on visuospatial attention. A region lateral to the intraparietal sulcus [inferior parietal lobule complex (IPLC)] and two regions in the medial PPC [precuneus complex (PCC) and posterior cingulate/retrosplenial cortex (pC/Rsp)] showed strong retrieval success effects for both picture and sound stimuli. Study 2 explored a recognition task with varied response contingencies to investigate whether these retrieval success effects are dependent on motor intentions. In one condition, subjects responded to both old and new items. In two other conditions, subjects responded only to old or only to new items. IPLC, PCC, and pC/Rsp continued to show retrieval success effects with similar magnitudes for all response contingencies, including a condition in which no responses were made to old items. In a third study, IPLC and PCC activity was modulated at retrieval based on levels of processing at study, suggesting sensitivity to memory demands. These studies demonstrate that retrieval success effects in lateral and medial PPC regions are not affected by manipulations predicted by classical theories of PPC function but can be modulated by memory-related manipulations. PPC regions thus have prominent response properties associated with memory, which may arise through interactions with medial temporal cortex.

Neuropsychological Functioning Associated with High-Altitude Exposure

This article focuses on neuropsychological functioning at moderate, high, and extreme altitude. This article summarizes the available literature on respiratory, circulatory, and brain determinants on adaptation to hypoxia that are hypothesized to be responsible for neuropsychological impairment due to altitude. Effects on sleep are also described. At central level, periventricular focal damages (leuko-araiosis) and cortical atrophy have been observed. Frontal lobe and middle temporal lobe alterations are also presumed. A review is provided regarding the effects on psychomotor performance, perception, learning, memory, language, cognitive flexibility, and metamemory. Increase of reaction time and latency of P300 are observed. Reduced thresholds of tact, smell, pain, and taste, together with somesthetic illusions and visual hallucinations have been reported. Impairment in codification and short-term memory are especially noticeable above 6,000 m. Alterations in accuracy and motor speed are identified at lower altitudes. Deficits in verbal fluency, language production, cognitive fluency, and metamemory are also detected. The moderating effects of personality variables over the above-mentioned processes are discussed. Finally, methodological flaws found in the literature are detailed and some applied proposals are suggested.

Functional deactivations: change with age and dementia of the Alzheimer type

Young adults typically deactivate specific brain regions during active task performance. Deactivated regions overlap with those that show reduced resting metabolic activity in aging and dementia, raising the possibility of a relation. Here, the magnitude and dynamic temporal properties of these typically deactivated regions were explored in aging by using functional MRI in 82 participants. Young adults (n = 32), older adults without dementia (n = 27), and older adults with early-stage dementia of the Alzheimer type (DAT) (n = 23) were imaged while alternating between blocks of an active semantic classification task and a passive fixation baseline. Deactivation in lateral parietal regions was equivalent across groups; in medial frontal regions, it was reduced by aging but was not reduced further by DAT. Of greatest interest, a medial parietal/ posterior cingulate region showed differences between young adults and older adults without dementia and an even more marked difference with DAT. The temporal profile of the medial parietal/posterior cingulate response suggested that it was initially activated by all three groups, but the response in young adults quickly reversed sign, whereas DAT individuals maintained activation throughout the task block. Exploratory whole-brain analyses confirmed the importance of medial parietal/posterior cingulate cortex differences in aging and DAT. These results introduce important opportunities to explore the functional properties of regions showing deactivations, how their dynamic functional properties relate to their baseline metabolic rates, and how they change with age and dementia.

FDG-PET findings in the Wernicke-Korsakoff syndrome

This study reports FDG-PET findings in Wernicke-Korsakoff patients. Twelve patients suffering amnesia arising from the Korsakoff syndrome were compared with 10 control subjects without alcohol-related disability. Subjects received [18F]-fluorodeoxyglucose (FDG-PET) imaging as well as neuropsychological assessment and high-resolution MR imaging with volumetric analysis. Volumetric MRI analysis had revealed thalamic and mamillary body atrophy in the patient group as well as frontal lobe atrophy with relative sparing of medial temporal lobe structures. Differences in regional metabolism were identified using complementary region of interest (ROI) and statistical parametric mapping (SPM) approaches employing either absolute methods or a reference region approach to increase statistical power. In general, we found relative hypermetabolism in white matter and hypometabolism in subcortical grey matter in Korsakoff patients. When FDG uptake ratios were examined with occipital lobe metabolism as covariate reference region, Korsakoff patients showed widespread bilateral white matter hypermetabolism on both SPM and ROI analysis. When white matter metabolism was the reference covariate; Korsakoff patients showed relative hypometabolism in the diencephalic grey matter, consistent with their known underlying neuropathology, and medial temporal and retrosplenial hypometabolism, interpreted as secondary metabolic effects within the diencephalic-limbic memory circuits. There was also evidence of a variable degree of more general frontotemporal neocortical hypometabolism on some, but not all, analyses.

Lactate: a preferred fuel for human brain metabolism in vivo

Recent in vitro studies suggest that lactate, rather than glucose, may be the preferred fuel for neuronal metabolism. The authors examined the effect of lactate on global brain glucose uptake in euglycemic human subjects using 18 fluoro-deoxyglucose (FDG) positron emission tomography (PET). Eight healthy men, aged 40 to 54 years, underwent a 60-minute FDG-PET scan on two occasions in random order. On one occasion, 6.72% sodium lactate was infused at a rate of 50 micro mol. kg-1. min-1 for 20 minutes and then reduced to 30 micro mol. kg-1. min-1; 1.4% sodium bicarbonate was infused as a control on the other occasion. Plasma glucose levels were not different between the two groups (5.3 +/- 0.23 and 5.3 +/- 0.24 mmol/L, P = 0.55). Plasma lactate was significantly elevated by lactate infusion (4.08 +/- 0.35 vs. 0.63 +/- 0.22 mmol/L, P < 0.0005. The whole-brain rate of glucose uptake was significantly reduced by approximately 17% during lactate infusion (0.195 +/- 0.022 vs. 0.234 +/- 0.020 micro mol. g-1. min-1, P = 0.001). The authors conclude that, in vivo in humans, circulating lactate is used by the brain at euglycemia, with sparing of glucose.

Positron emission tomographic study of post-ischaemic-hypoxic amnesia

BACKGROUND

Despite extensive research, it still remains controversial as to what the precise location of the critical lesions underlying amnesia actually is. The amnesic syndrome is believed to be heterogeneous and due to several distinct functional deficits.

PATIENTS AND METHODS

Two patients, a 45-year-old woman and a 56-year-old man, with sudden cardiopulmonary arrest and successful resuscitation, were left with a clear amnesic syndrome as main neurological sequela. During their revalidation period, they underwent a positron emission tomographic (PET) examination, utilizing the (13)NH(3) bolus technique at rest and after intravenous acetazolamide administration.

RESULTS

Both PET studies showed more or less similar features with a decrease in regional cerebral blood flow (rCBF) in the frontal, temporal and parietal lobes. In addition, the rCBF was increased in both thalami of the 45-year-old woman and in the striata of the 56-year-old man. Acetazolamide vasoreactivity was most lost in the frontal lobes.

CONCLUSIONS

In the present PET study, we demonstrated that destruction of the inhibitory pathways to the thalamus and basal ganglia by ischaemic-hypoxic frontal lesions could be one of the mechanisms leading to amnesia.

Advanced brain imaging procedures and human memory disorder

The impact of advanced brain imaging procedures in the field of human memory disorder is reviewed, with particular emphasis on current and potential applications that may impact upon the diagnosis and management of memory-disordered patients. While both advanced structural, resting physiological and functional physiological brain imaging procedures have been applied to conditions where memory disorder is a major feature, the specific implications of research findings for diagnosis and treatment in routine clinical practice remain tentative and promising, but not yet substantive enough to inform clinical decisions to a significant degree. In terms of diagnostic applications, several promising areas include dementia, epilepsy, and transient amnesic states. In the case of applications in treatment settings, advanced brain imaging procedures may help to monitor neural correlates of spontaneous recovery or progression of memory function, and may also help in the planning and monitoring of therapeutic intervention.

The role of insulin in human brain glucose metabolism: an 18fluoro-deoxyglucose positron emission tomography study

The effect of basal insulin on global and regional brain glucose uptake and metabolism in humans was studied using 18-fluorodeoxyglucose and positron emission tomography (FDG-PET). Eight healthy male volunteers aged 49.3 +/- 5.1 years were studied twice in random order. On each occasion, they received an infusion of 0.1 mg. kg(-1). min(-1) somatostatin to suppress endogenous insulin production. In one study 0.3 mU. kg(-1). min(-1) insulin was infused to replace basal circulating insulin levels, and in the other study a saline infusion was used as control. We sought stimulatory effects of basal insulin on brain glucose metabolism particularly in regions with deficiencies in the blood-brain barrier and high density of insulin receptors. Insulin levels were 27.07 +/- 1.3 mU/l with insulin replacement and 3.51 +/- 0.4 mU/l without (P = 0.001). Mean global rate of brain glucose utilization was 0.215 +/- 0.030 mmol. kg(-1). min(-1) without insulin and 0.245 +/- 0.021 mmol. kg(-1). min(-1) with insulin (P = 0.008, an average difference of 15.3 +/- 12.5%). Regional analysis using statistical parametric mapping showed that the effect of basal insulin was significantly less in the cerebellum (Z = 5.53, corrected P = 0.031). We conclude that basal insulin has a role in regulating global brain glucose uptake in humans, mostly marked in cortical areas.

Changes in regional brain (18)F-fluorodeoxyglucose uptake at hypoglycemia in type 1 diabetic men associated with hypoglycemia unawareness and counter-regulatory failure

We examined the effects of acute moderate hypoglycemia and the condition of hypoglycemia unawareness on regional brain uptake of the labeled glucose analog [(18)F]fluorodeoxyglucose (FDG) using positron emission tomography (PET). FDG-PET was performed in diabetic patients with (n = 6) and without (n = 7) hypoglycemia awareness. Each patient was studied at plasma glucose levels of 5 and 2.6 mmol/l, applied by glucose clamp techniques, in random order. Hypoglycemia-unaware patients were asymptomatic during hypoglycemia, with marked attenuation of their epinephrine responses (mean [+/- SD] peak of 0.77 +/- 0.39 vs. 7.52 +/- 2.9 nmol/l; P < 0.0003) and a reduced global brain FDG uptake ([mean +/- SE] 2.592 +/- 0.188 vs. 2.018 +/- 0.174 at euglycemia; P = 0.027). Using statistical parametric mapping (SPM) to analyze images of FDG uptake, we identified a subthalamic brain region that exhibited significantly different behavior between the aware and unaware groups. In the aware group, there was little change in the normalized FDG uptake in this region in response to hypoglycemia ([mean +/- SE] 0.654 +/- 0.016 to 0.636 +/- 0.013; NS); however, in the unaware group, the uptake in this region fell from 0.715 +/- 0.015 to 0.623 +/- 0.012 (P = 0.001). Our data were consistent with the human hypoglycemia sensor being anatomically located in this brain region, and demonstrated for the first time a change in its metabolic function associated with the failure to trigger a counter-regulatory response.

Remembering familiar people: the posterior cingulate cortex and autobiographical memory retrieval

Most functional imaging studies of memory retrieval investigate memory for standardized laboratory stimuli. However, naturally acquired autobiographical memories differ from memories of standardized stimuli in important ways. Neuroimaging studies of natural memories may reveal distinctive patterns of brain activation and may have particular value in assessing clinical disorders of memory. This study used functional magnetic resonance imaging to investigate brain activation during successful retrieval of autobiographical memories elicited by name-cued recall of family members and friends. The caudal part of the left posterior cingulate cortex was the most strongly activated region and was significantly activated in all eight subjects studied. Most subjects also showed significant activation of the left anterior orbitomedial, anterior middle frontal, precuneus, cuneus, and posterior inferior parietal cortices, and the right posterior cingulate and motor cortices.Our findings are consistent with prior studies showing posterior cingulate cortex activation during autobiographical memory retrieval. This region is also consistently activated during retrieval of standardized memory stimuli when experimental designs emphasizing successful retrieval are employed. Our results support the hypothesis that the posterior cingulate cortex plays an important role in successful memory retrieval. The posterior cingulate cortex has strong reciprocal connections with entorhinal and parahippocampal cortices. Studies of early Alzheimer's disease, temporal lobectomy, and hypoxic amnesia show that hypometabolism of the posterior cingulate cortex is an early and prominent indicator of pathology in these patients. Our findings suggest that autobiographical memory retrieval tasks could be used to probe the functional status of the posterior cingulate cortex in patients with early Alzheimer's disease or at risk for that condition.

Structural MRI volumetric analysis in patients with organic amnesia, 2: correlations with anterograde memory and executive tests in 40 patients

BACKGROUND

Cognitive-MRI correlations have often been studied in disorders in which there are multiple cognitive deficits and widespread cortical atrophy, such as Alzheimer's dementia. In such circumstances, the interpretation of any single cognitive-structural correlation is equivocal. Only by measuring differing cognitive functions and a wide range of brain structures in patients with a varying distribution of lesions or atrophy can specific brain-cognitive relations be determined in neurological disorder.

METHOD

In the present study, a clear set of anatomical criteria and detailed MRI segmentation procedures were applied to measure whole brain, and left and right frontal, temporal lobe, anterolateral and medial temporal volumes, as well as thalamic cross sectional areas in 40 patients with organic amnesia (from various diseases) and 10 healthy controls.

RESULTS

Within the total patient group, anterograde memory measures correlated significantly with medial temporal, hippocampal, and thalamic measurements. A spatial memory measure correlated significantly with hippocampal volume, and temporal context memory with frontal volume. After a factor analysis of the cognitive measures, the association between anterograde memory and hippocampal volume was corroborated. Forgetting rates and subjective memory evaluations did not show any significant MR correlations and, of executive tests employed, only card sorting categories correlated significantly with frontal volume.

CONCLUSION

Loss of volume in key brain structures (for example, hippocampus, thalamus) is detectable on quantitative MRI, and this loss of volume correlates significantly with impaired performance on measures of anterograde memory function. Correlations with hippocampal volume did not indicate a specific role in either recall or verbal memory, as opposed to recognition or visual memory.

Voxel-Based Mapping of Brain Hypometabolism in Permanent Amnesia with PET

In this study, we used voxel-based mapping methods to compare the resting cerebral metabolic rate of glucose (CMRglc) measured with PET in five patients with permanent amnesia (three with chronic Wernicke-Korsakoff and two with postanoxia syndrome) to that of nine healthy age-matched subjects. We assessed (i) a group pattern of relative hypometabolism; and (ii) the consistency of this group pattern, if any, in individual subjects, according to etiology. The results from the group analysis documented that permanent amnesia is associated with hypometabolism in the thalamus, posterior cingulate cortex, and mesial prefrontal cortex (near the anterior cingulate gyrus), bilaterally, as well as in the left supramarginal and middle temporal gyri. The individual analysis showed that this group pattern was found in essentially each patient, regardless of the cause of amnesia. Thus, permanent amnesia is subtended by dysfunction in structures belonging to Papez/limbic circuits as well as in left-hemisphere areas typically concerned with verbal functions, probably through a mechanism of thalamo-cortical disconnection and possibly involved in retrograde amnesia. The use of a voxel-based method allowed us to map a common network of synaptic dysfunction in a neuropsychological syndrome regardless of etiology. Our results indicate that this should be a powerful method in functional neuropsychology.