The pattern of function-related regional cerebral blood flow investigated by single photon emission tomography with 99mTc-HMPAO in patients with presenile Alzheimer's disease and Korsakoff's psychosis

Aging with alcohol-related brain damage: Critical brain circuits associated with cognitive dysfunction

Alcoholism is associated with brain damage and impaired cognitive functioning. The relative contributions of different etiological factors, such as alcohol, thiamine deficiency and age vulnerability, to the development of alcohol-related neuropathology and cognitive impairment are still poorly understood. One reason for this quandary is that both alcohol toxicity and thiamine deficiency produce brain damage and cognitive problems that can be modulated by age at exposure, aging following alcohol toxicity or thiamine deficiency, and aging during chronic alcohol exposure. Pre-clinical models of alcohol-related brain damage (ARBD) have elucidated some of the contributions of ethanol toxicity and thiamine deficiency to neuroinflammation, neuronal loss and functional deficits. However, the critical variable of age at the time of exposure or long-term aging with ARBD has been relatively ignored. Acute thiamine deficiency created a massive increase in neuroimmune genes and proteins within the thalamus and significant increases within the hippocampus and frontal cortex. Chronic ethanol treatment throughout adulthood produced very minor fluctuations in neuroimmune genes, regardless of brain region. Intermittent "binge-type" ethanol during the adolescent period established an intermediate neuroinflammatory response in the hippocampus and frontal cortex, that can persist into adulthood. Chronic excessive drinking throughout adulthood, adolescent intermittent ethanol exposure, and thiamine deficiency all led to a loss of the cholinergic neuronal phenotype within the basal forebrain, reduced hippocampal neurogenesis, and alterations in the frontal cortex. Only thiamine deficiency results in gross pathological lesions of the thalamus. The behavioral impairment following these types of treatments is hierarchical: Thiamine deficiency produces the greatest impairment of hippocampal- and prefrontal-dependent behaviors, chronic ethanol drinking ensues mild impairments on both types of tasks and adolescent intermittent ethanol exposure leads to impairments on frontocortical tasks, with sparing on most hippocampal-dependent tasks. However, our preliminary data suggest that as rodents age following adolescent intermittent ethanol exposure, hippocampal functional deficits began to emerge. A necessary requirement for the advancement of understanding the neural consequences of alcoholism is a more comprehensive assessment and understanding of how excessive alcohol drinking at different development periods (adolescence, early adulthood, middle-aged and aged) influences the trajectory of the aging process, including pathological aging and disease.

Vascular Dysfunction in Alzheimer's Disease: A Prelude to the Pathological Process or a Consequence of It?

Alzheimer's disease (AD) is the most prevalent form of dementia. Despite decades of research following several theoretical and clinical lines, all existing treatments for the disorder are purely symptomatic. AD research has traditionally been focused on neuronal and glial dysfunction. Although there is a wealth of evidence pointing to a significant vascular component in the disease, this angle has been relatively poorly explored. In this review, we consider the various aspects of vascular dysfunction in AD, which has a significant impact on brain metabolism and homeostasis and the clearance of β-amyloid and other toxic metabolites. This may potentially precede the onset of the hallmark pathophysiological and cognitive symptoms of the disease. Pathological changes in vessel haemodynamics, angiogenesis, vascular cell function, vascular coverage, blood-brain barrier permeability and immune cell migration may be related to amyloid toxicity, oxidative stress and apolipoprotein E (APOE) genotype. These vascular deficits may in turn contribute to parenchymal amyloid deposition, neurotoxicity, glial activation and metabolic dysfunction in multiple cell types. A vicious feedback cycle ensues, with progressively worsening neuronal and vascular pathology through the course of the disease. Thus, a better appreciation for the importance of vascular dysfunction in AD may open new avenues for research and therapy.

Neural Correlate of Anterograde Amnesia in Wernicke-Korsakoff Syndrome

The neural correlate of anterograde amnesia in Wernicke-Korsakoff syndrome (WKS) is still debated. While the capacity to learn new information has been associated with integrity of the medial temporal lobe (MTL), previous studies indicated that the WKS is associated with diencephalic lesions, mainly in the mammillary bodies and anterior or dorsomedial thalamic nuclei. The present study tested the hypothesis that amnesia in WKS is associated with a disrupted neural circuit between diencephalic and hippocampal structures. High-density evoked potentials were recorded in four severely amnesic patients with chronic WKS, in five patients with chronic alcoholism without WKS, and in ten age matched controls. Participants performed a continuous recognition task of pictures previously shown to induce a left medial temporal lobe dependent positive potential between 250 and 350 ms. In addition, the integrity of the fornix was assessed using diffusion tensor imaging (DTI). WKS, but not alcoholic patients without WKS, showed absence of the early, left MTL dependent positive potential following immediate picture repetitions. DTI indicated disruption of the fornix, which connects diencephalic and hippocampal structures. The findings support an interpretation of anterograde amnesia in WKS as a consequence of a disconnection between diencephalic and MTL structures with deficient contribution of the MTL to rapid consolidation.

Function and dysfunction of prefrontal brain circuitry in alcoholic Korsakoff's syndrome

The signature symptom of alcohol-induced persisting amnestic disorder, more commonly referred to as alcoholic Korsakoff's syndrome (KS), is anterograde amnesia, or memory loss for recent events, and until the mid 20th Century, the putative brain damage was considered to be in diencephalic and medial temporal lobe structures. Overall intelligence, as measured by standardized IQ tests, usually remains intact. Preservation of IQ occurs because memories formed before the onset of prolonged heavy drinking--the types of information and abilities tapped by intelligence tests--remain relatively well preserved compared with memories recently acquired. However, clinical and experimental evidence has shown that neurobehavioral dysfunction in alcoholic patients with KS does include nonmnemonic abilities, and further brain damage involves extensive frontal and limbic circuitries. Among the abnormalities are confabulation, disruption of elements of executive functioning and cognitive control, and emotional impairments. Here, we discuss the relationship between neurobehavioral impairments in KS and alcoholism-related brain damage. More specifically, we examine the role of damage to prefrontal brain systems in the neuropsychological profile of alcoholic KS.

Neuroimaging of Wernicke's encephalopathy and Korsakoff's syndrome

There is considerable evidence that neuroimaging findings can improve the early diagnosis of Wernicke's encephalopathy (WE) in clinical settings. The most distinctive neuroimaging finding of acute WE are cytotoxic edema and vasogenic edema, which are represented by bilateral symmetric hyperintensity alterations on T2-weighted MR images in the periphery of the third ventricle, periaqueductal area, mammillary bodies and midbrain tectal plate. An initial bout of WE can result in Korsakoff's syndrome (KS), but repeated bouts in conjunction with its typical comorbidity, chronic alcoholism, can result in signs of tissue degeneration in vulnerable brain regions. Chronic abnormalities identified with neuroimaging enable examination of brain damage in living patients with KS and have expanded the understanding of the neuropsychological deficits resulting from thiamine deficiency, alcohol neurotoxicity, and their comorbidity. Brain structure and functional studies indicate that the interactions involving the thalamus, mammillary bodies, hippocampus, frontal lobes, and cerebellum are crucial for memory formation and executive functions, and the interruption of these circuits by WE and chronic alcoholism can contribute substantially to the neuropsychological deficits in KS.

Biomarkers of Alzheimer's disease

Although a battery of neuropsychological tests is often used in making a clinical diagnosis of Alzheimer's disease (AD), definitive diagnosis still relies on pathological evaluation at autopsy. The identification of AD biomarkers may allow for a less invasive and more accurate diagnosis as well as serve as a predictor of future disease progression and treatment response. Importantly, biomarkers may also allow for the identification of individuals who are already developing the underlying pathology of AD such as plaques and tangles yet who are not yet demented, i.e. "preclinical" AD. Attempts to identify biomarkers have included fluid and imaging studies, with a number of candidate markers showing significant potential. More recently, better reagent availability and novel methods of assessment have further spurred the search for biomarkers of AD. This review will discuss promising fluid and imaging markers to date.

Comparisons of Korsakoff and non-Korsakoff alcoholics on neuropsychological tests of prefrontal brain functioning

BACKGROUND

Evidence suggests that alcoholics exhibit particular deficits in brain systems involving the prefrontal cortex, but few studies have directly compared patients with and without Korsakoff's syndrome on measures of prefrontal integrity.

METHODS

Neuropsychological tasks sensitive to dysfunction of frontal brain systems were administered, along with standard tests of memory, intelligence, and visuospatial abilities, to 50 healthy, abstinent, nonamnesic alcoholics, 6 patients with alcohol-induced persisting amnestic disorder (Korsakoff's syndrome), 6 brain-damaged controls with right hemisphere lesions, and 82 healthy nonalcoholic controls.

RESULTS

Korsakoff patients were impaired on tests of memory, fluency, cognitive flexibility, and perseveration. Non-Korsakoff alcoholics showed some frontal system deficits as well, but these were mild. Cognitive deficits in non-Korsakoff alcoholics were related to age, duration of abstinence (less than 5 years), duration of abuse (more than 20 years), and amount of alcohol intake.

CONCLUSIONS

Abnormalities of frontal system functioning are most apparent in alcoholics with Korsakoff's syndrome. In non-Korsakoff alcoholics, factors contributing to cognitive performance are age, duration of abstinence, duration of alcoholism, and amount of alcohol consumed.

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.

Korsakoff syndrome following chronic subdural hematoma

We describe a patient who developed Korsakoff syndrome following a spontaneous chronic subdural hematoma. The present case demonstrates persistence of both amnesia and confabulation long after recovery from the acute phase of spontaneous chronic subdural hematoma. There are few reports describing persistent amnesia with confabulation following brain damage. We considered that chronic subdural hematoma in the bilateral frontal and temporal lobes caused amnesia and confabulations, and these conditions persisted as a result of organic atrophic changes of both the frontal and temporal lobes due to long-term compression by chronic subdural hematoma.

Cerebral perfusion defects in combined cocaine and alcohol dependence

BACKGROUND

Cocaine abuse has been associated with widely distributed areas of significant cerebral blood flow (CBF) reductions or hypo-perfusion as well as CBF hyper-perfusion, but these perfusion abnormalities have not been examined using newer technologies such as statistical parametric mapping (SPM). These areas of abnormal CBF may be more likely among those who abuse cocaine and alcohol together.

METHODS

Using SPECT with HMPAO for CBF we compared proportional scaling (PS) to histogram normalization (HEQ) in SPM among 20 controls and 32 recently abstinent cocaine abusers. We then separated the cocaine abusers into two groups (12 cocaine plus alcohol abusers and 20 cocaine alone abusers) and compared both groups to the 20 controls for brain areas of hypo- and hyper-perfusion.

RESULTS

Sensitivity to hypo-perfusion was greater with HEQ than PS. Hypo-perfused areas were more likely in the 12 alcohol plus cocaine abusers than in the 20 cocaine alone abusers or 20 controls, and hyper-perfused areas were significantly more likely among the cocaine abusers than controls. The type of CBF abnormality varied by brain location with hypo-perfusion significantly more likely in occipital and temporal cortex or cerebellum and hyper-perfusion more likely in frontal and parietal cortex.

CONCLUSIONS

These abnormalities in brain perfusion are consistent with previous non-SPM approaches that showed more hypo-perfusion in cocaine abusers than controls and appear to reflect vasospasm and potential compensations in cerebral blood flow.

Structural and functional neuroimaging findings in substance-related disorders

Intoxication with alcohol results in depressed global glucose metabolism that continues into the stages of withdrawal and abstinence. The decrease in metabolism, however, is not equal across the brain, with certain regions more affected than others. Such a pattern of disturbance suggests that the effect of alcohol on the brain cannot simply be a nonspecific depressant effect secondary to decreased blood flow or glucose transport into the cells but may be related to the dysfunction of the various neurotransmitter systems. Different authors have suggested the dysfunction to be related to the GABAergic, cholinergic, and dopaminergic systems. Long-term alcoholism is associated with atrophy of several brain regions. The frontal lobes and limbic structures seem to be most vulnerable. The data are encouraging with regard to the normalization in brain metabolism and in size of vulnerable brain regions with continued abstinence. In addition to findings of improvement in cognitive functioning and many health parameters, these findings arm clinicians with further data on the benefits of abstinence in the struggle to aid patients in maintaining their sobriety. Several areas remain to be addressed. In particular, clinicians are in need of data, neuroimaging and otherwise, that serve as prognostic indicators, thus allowing patients at higher risk for relapse to be identified and provided with more intensive treatment. A similar need exists for indicators of diagnostic heterogeneity that would guide the development of more highly tailored treatment regimens for identified subgroups of patients. Currently, we have rudimentary knowledge of the gender differences of the effects of alcohol and cocaine on the brain.

Brain imaging. Functional consequences of ethanol in the central nervous system

In recent years, sophisticated methods have been developed to view structure and function within the living brain. Functional imaging methods are used to visualize dynamic chemical processes that are linked to brain activity. Increased neural activity, for example, leads to greater glucose and oxygen consumption and greater regional rates of blood flow to meet elevated energy demands. Mapping these changes provides quantitative visual descriptions of localized changes in brain activity that result from behavioral or pharmacological manipulations. This chapter first describes several current methods and how they are used to study the effects of alcohol on brain function. In the second part, the effects of acute intoxication are discussed with emphasis on the complex nature of alcohol's effects in the central nervous system, which depend on dose, time since administration, and environmental context. In the final part, the functional consequences of long-term exposure to alcohol as well as diseases associated with chronic alcoholism are reviewed.

Regional cerebral blood flow during acute and chronic abstinence from combined cocaine-alcohol abuse

Regional cerebral blood flow (rCBF) was assessed using SPECT and HMPAO in ten cocaine abusers within 72 h of last cocaine use and then after 21 days of abstinence. In comparison to normals the cocaine abusers had significantly reduced rCBF in 11 of 14 brain regions with the largest reductions in the frontal and parietal cortex and greater rCBF in the brain stem. These perfusion defects appeared to be primarily due to combined alcohol and cocaine abuse and frontal but not parietal defects appeared to resolve partially during 21 days of abstinence.

Two circuits to convert short-term memory into long-term memory

According to a brain model, encoding synapses record presynaptic axonal 'on-off' patterns as memory, and modulating synapses convert short-term memory into long-term memory by helping encoding synapses develop long-term potentiation and depression. Sensory organs conduct sounds and images as series of axonal 'on-off' patterns to encoding synapses of perceptive cortices where the patterns are recorded, computed, and rerouted to mesotemporal lobes, hippocampal formations and higher cortical centers. Mesotemporal lobes and hippocampal formations compute and convey the 'on-off' patterns to dorsomedial thalamic nuclei (circuit A), septal nuclei and mammillary bodies (circuit B), where the patterns are computed and conveyed to prefrontal lobes (circuit A) and anterior thalamic nuclei (circuit B) respectively. Anterior thalamic nuclei project axonal 'on-off' patterns to cingulate gyri that compute and convey the patterns to prefrontal lobes. Finally, prefrontal lobes send modulating axons to encoding synapses of perceptive cortices. Amnesia of Korsakoff's syndrome results from unilateral dysfunction of circuit A and contralateral dysfunction of circuit B, or bilateral dysfunction of either. The fact that there is more severe memory deficit in Alzheimer's disease than in Korsakoff's syndrome suggests that the former has a wider spread of failing synapses besides circuit A and circuit B.

123Iodo-MK-801: a spect agent for imaging the pattern and extent of glutamate (NMDA) receptor activation in Alzheimer's disease

Glutamate, and the NMDA glutamate receptor, may be involved in Alzheimer's Disease (AD). Reductions in NMDA receptors are found in AD, possibly contributing to memory deficits. However the NMDA receptor is involved in excitotoxicity, which may play a role in cell death and the production of neurofibrillary tangles in AD; although with lower levels of glutamate than occur in cerebral ischaemia. Therefore reductions in the NMDA receptor may worsen memory deficit in AD, but increased stimulation of the receptor may contribute to the progress of the disease. MK-801 has been used to image excessive glutamate activation following ischaemia in rats. However, it is unclear how effective MK-801 is in conditions with lower levels of glutamate release. This study attempts to gain insight into the utility of the tracer in these conditions, exploring glutamatergic mechanisms in AD. It describes the retention and elimination of 123iodo-MK-801 in five AD and five control subjects, comparing this to regional cerebral blood flow (rCBF). The initial uptake of 123I-MK-801 is dominated by delivery of the ligand. However, despite significant reductions in rCBF in the AD patients, there is no significant difference in the uptake of 123I-MK-801. This suggests increased retention of 123I-MK-801 in the AD patients. In addition the washout of 123I-MK-801 was less in the AD patients, again suggesting increased retention, although this only reached significance in one region. Theses data hint at possible increases in NMDA activation in AD but ultimately 123I-MK-801 does not provide a sufficiently accurate measurement to demonstrate this conclusively. Further NMDA ligands are now at a late stage of development and may provide more conclusive answers to the role of glutamate in AD.

Association between medial temporal lobe atrophy on CT and parietotemporal uptake decrease on SPECT in Alzheimer's disease

OBJECTIVES

Alzheimer's disease is the most frequent cause of degenerative dementia. Despite the available diagnostic criteria, improvement of diagnosic accuracy is still required. The aim of this prospective study was to assess in a large population of patients referred to a memory clinic the diagnostic value of the combination of medial temporal lobe atrophy on temporal oriented CT and decreased temporoparietal uptake on HMPAO single photon emission tomography (SPECT).

METHODS

The study was conducted in 125 patients aged 51-93: 64 with probable Alzheimer's disease (Mean (SD) mini mental state examination (MMSE)=18.34 (6.93)), duration of disease=6.48 (2.93) years, 13 possible Alzheimer's disease (MMSE=21.58 (5.48), duration of disease=6.08 (2.56)), 48 patients with miscellaneous memory disorders (MMSE=21.98 (6.10), duration the disease = 6.85 (3.91)).

RESULTS

For the diagnosis of probable Alzheimer's disease, the sensitivity of this association was 0.56, the specificity 0.93, the positive predictive value 0.95, and the negative predictive value 0.45. The diagnosic accuracy was 0.68. Both medial temporal atrophy and parietotemporal decrease in uptake were present in four of 13 patients with possible Alzheimer's disease and 11 of 48 with miscellaneous memory disorders. The association was absent in 27 of 29 patients with frontotemporal dementia. In mild stages (MMSE>18; n = 32), the sensitivity of the association was 0.34, the specificity 0.93, the positive predictive value 0.85, and the negative predictive value 0.57. The diagnosic accuracy was 0.53.

CONCLUSION

This association, although not sensitive, helps to select patients with high probability of Alzheimer's disease at an early stage which can be of interest for clinical and research purposes.

Regional cerebral blood flow and oxygen metabolism in a patient with Korsakoff syndrome

We report a functional neuroimaging study of a patient clinically diagnosed with Korsakoff syndrome. Positron emission tomography (PET) with the 15O inhalation method showed decreased regional cerebral blood flow (rCBF) and decreased regional cerebral metabolic ratio for oxygen (rCMRO2) in the bilateral fronto-temporal areas and in the left thalamus. These results suggest that dysfunction of the frontal-thalamic neural network plays a role in the disturbance of Korsakoff syndrome.

What's wrong and what's right in neuropsychology and neuropsychiatry

There has been a recent converging of interests by psychiatrists and psychologists in subjective mental phenomena. Examples of topics where these converging interests arise include the relationship of confabulation and delusional memories, the nature of face-processing deficits in prosopagnosia and the Capgras delusion, and hierarchial models of psychological function. These developments are very much welcomed; but the over-interpretation of neuropsychological test findings in neuropsychiatry, and the occasional failure to take account of clinical context (particularly the psychiatric background) in neuropsychology, are also noted. Cognitive neuropsychiatry appears to have emerged as a label to identify this converging of interests, modelling itself on cognitive neuropsychology. The potential benefits and limitations of such an approach are discussed.

Alzheimer's disease risk factors as related to cerebral blood flow

Inconsistencies within results of case-control studies on Alzheimer's disease risk factors led to a search of the literature for a potential cofactor. Reduced cerebral blood flow was selected and literature was surveyed for evidence of a cerebral blood flow linkage with the more than 40 putative risks. Alcohol abuse, depression, head trauma, underactivity, old age, sleep disturbance, glucose utilization, Down's syndrome, and Parkinson's disease are risk factors where an association with reduced cerebral blood flow is documented. Studies were cited showing that improved cerebral blood flow is associated with factors thought to be helpful in Alzheimer's disease, such as education or occupational attainment, exercise, headache, smoking, and arthritis/anti-inflammatory drugs to the extent that aspirin is used. Sugar consumption is identified as a potential risk factor with glucose management in Alzheimer's disease also shown to involve reduced cerebral blood flow. An hypothesis is developed showing how compromised regional cerebral blood flow could fit as a cofactor for genetic, autoimmune, and neurotoxic aspects of Alzheimer's disease.

Longitudinal changes in cognitive function and regional cerebral function in Alzheimer's disease: a SPECT blood flow study

In Alzheimer's disease (AD), SPECT imagining of regional cerebral blood flow (rCBF) has emphasized deficits in the posterior association cortex. Previous studies have shown an association between these deficits and cognitive performance, both on overall cognitive tests and more specific tests such as praxis and language. Frontal deficits have been reported in more severe patients. This has led to the conclusion that the deficit in AD, at least with functional neuroimaging, starts in the posterior association cortex, and later in the disease process "spreads" to involve the frontal cortex. This study set out to measure, in a group of AD patients, the change over time of cognitive performance and the pattern of functional deficit measured by neuroimaging. Change in function was measured using 99TCm-HMPAO and SPECT and change in cognitive function using the CAMCOG. Two time points were used, 0 and 2 years. Twenty-four patients satisfying the DSM-III R criteria for probable AD were studied, nine of whom were subsequently diagnosed as having AD at post-mortem. The most striking finding was the effect that decreases in frontal lobe function had on cognitive function. A similar study by the same group, using the same techniques and many of the same patients but at only one time point, showed a correlation between cognitive function and rCBF in the parietal and posterior temporal lobes. This suggests that as AD patients deteriorate from unaffected to mild or moderately affected, the posterior association cortex exerts the greatest effect on cognitive deficit. In this longitudinal study, we found, using a MANOVA, that there were significant decreases over time for all the cortical regions studied, but that no region decreased significantly more than any other. In addition we found a correlation between change in frontal rCBF and change in cognitive function (both overall cognitive function and the CAMCOG sub tests of language and praxis). These data suggest, in contrast to the previous study, that as the disease progresses from mild or moderate to moderate or severe, the frontal cortex exerts the greatest effect on cognitive decline. These data support the concept of the deficit in functional imaging spreading from posterior to anterior as the disease progresses. However, both the initial pattern of deficit and the change over time were very heterogeneous when examined qualitatively. A posterior to anterior spread is the predominant pattern for the group as a whole, but individual patients, and possibly groups of patients, may well show alternative patterns.

Neuropsychology of memory and SPECT in the diagnosis and staging of dementia of Alzheimer type

We studied the role of neuropsychology and SPECT imaging in the diagnosis and staging of dementia of Alzheimer type (DAT) in 33 patients with mild disease and 30 matched controls. Working, episodic, semantic and remote memory were assessed. For diagnosis, it was determined by logistic regression analysis that one of the memory tests (delayed verbal recall of the Doors and People Test) could correctly classify subjects as DAT or controls in 97% of cases. For staging, stepwise regression analysis using five of the memory tests could predict 70% of the variance in Mini Mental State Examination (MMSE) scores. The measures most useful for staging were tests of immediate recall, and tests of working, semantic and autobiographical memory. In a separate experiment, SPECT imaging on 31 of the above 33 patients and 24 different controls was used to address the issue of diagnosis and staging. 99Tc-HMPAO SPECT scans were analysed quantitatively to obtain measures of regional cerebral blood flow (rCBF). Logistic regression analysis showed that three of the SPECT regions of interest (left posterior temporal, right high frontal and right posterior temporal) could correctly classify subjects in 75% of cases. Of note was the fact that 39% of the DAT patients had normal SPECT scans. SPECT data were of limited use in modelling disease severity; only 38% of the variance in MMSE scores could be predicted from SPECT data. In addition, we found that the pattern of rCBF in DAT was much more heterogeneous than previously described.

A double-blind, placebo-controlled study of tacrine in patients with Alzheimer's disease using SPET

BACKGROUND

the effect of single-dose and long-term cholinergic enhancement with tacrine on regional cerebral perfusion was examined in patients with Alzheimer's disease using single-photon emission tomography (SPET).

METHOD

23 patients with probable Alzheimer's disease (DSM-III-R and NINCDS-ADRDA criteria) were scanned before and after a single oral dose of tacrine at the start of the study and again after 12 weeks of randomized, double-blind treatment with tacrine or placebo, using high resolution (99m)Tc-Exametazime SPET. Patients also underwent neuropsychological testing with the CAMCOG, the Mini-Mental State Examination and the Rivermead Behavioural Memory Test before and after 12 weeks of treatment.

RESULTS

occipital count ratios in all regions of interest declined by 3% over 12 weeks, indicating a progression of the disease. Acute tacrine challenge resulted in a 16% increase in the superior frontal and a 11% decrease in the anterior temporal cortex. The acute effects of tacrine were modified by 12 weeks of treatment, particularly in the medial frontal (cingulate) cortex where active treatment was associated with a reduced acute tacrine response. There were no changes in cognitive function associated with active treatment.

CONCLUSION

the study demonstrates the sensitivity of cerebral perfusion measures to changes during acute and medium-term tacrine treatment.

A single photon emission computed tomography study of cerebral regional perfusion changes induced by a learning task in subjects with mild memory impairment

Fifteen nondemented subjects with memory complaints underwent serial single photon emission computed tomography (SPECT) studies with technetium-99m-d, l-hexamethyl-propylene amine oxime (HMPAO) as tracer. Scans were carried out under a baseline conditions and during the learning phase of the Memory Efficiency Profile (MEP), a combined visual perception and memory task developed by Rey. Results indicate a positive correlation between activation, as indexed by HMPAO uptake, and neuropsychological assessment. Right temporal activation was correlated with MEP immediate recall. The right cerebellum was correlated with both MEP immediate and delayed recall. This study suggests that SPECT can show cortical activation during cognitive performance in subjects with mild memory impairment.

Neuropsychological tests and [99mTc]-HM PAO SPECT in the diagnosis of Alzheimer's dementia

Twenty-three patients with Alzheimer's dementia (AD) in relatively early stages and 40 patients with other cognitive disorders of vascular or degenerative aetiology underwent neuropsychological examination and [99mTc]-HM PAO single photon emission computed tomography (SPECT). In contrast to the commonly accepted notion of a posterior temporoparietal reduction of tracer uptake as the typical SPECT pattern of AD, the most consistent feature found in the SPECT images of our AD patients was a hippocampal uptake deficit, associated with a variable degree of temporal, parietal and frontal deficit (extending from the posterior to the anterior regions), according to the severity of the disease. These results support the theory of AD as a "hippocampal dementia", at least in the early stages. Neuropsychological tests were found to be somewhat more specific and more accurate than SPECT in distinguishing AD from non-AD cases.

Regional cerebral blood flow measured by 99mTc-HMPAO SPECT differs in subgroups of Alzheimer's disease

Alzheimer's disease (AD) is a heterogeneous entity. Identifying AD subtypes might have impact in patients' response to different treatment strategies. We designed a study to examine regional cerebral blood flow (rCBF) in AD subtypes. To identify AD subtypes, we performed a cluster analysis including performance on memory, language, visuospatial, praxic, and executive functions. The rCBF measured by 99mTc-HMPAO SPECT was referred to the cerebellum. We examined 35 patients fulfilling the NINCDS-ADRDA criteria of probable AD and 13 age and sex-matched healthy cognitively intact controls. AD patients were at the early stage of the disease, their mean Mini-Mental Status (MMS) score (S.D.) was 22.5 (3.6). The cluster analysis revealed two AD subgroups: AD1 (N = 12) and AD2 (N = 23). The subgroups did not differ in age, sex, or global clinical severity as assessed by MMS and Brief Cognitive Rating Scale (BCRS). Both subgroups had equally impaired memory. The AD2 group was inferior to the AD1 group on verbal, visuospatial, praxic, and executive functions. The AD1 group showed reduced rCBF ratios in the temporal and parietal cortices and the amygdala compared to controls. The AD2 group differed from controls in the rCBF ratios of frontal, temporal, parietal, occipital, basal ganglia, and amygdaloid regions bilateral and from AD1 in the rCBF ratios of frontal and temporal cortices. In AD patients, the rCBF ratios did not correlate with MMS or BCRS scores. In contrast, several significant correlations were found between decreases rCBF ratios and impairment of memory and other cognitive functions. In conclusion, a cluster analysis on neuropsychological test performance identified two AD subgroups that differed on the neuropsychological profile and on the rCBF in spite of similar global clinical severity.

A clinical perspective on SPECT

The potential clinical utility of SPECT (Single Photon Emission Computed Tomography) brain imaging to clarifying certain diagnostic dilemmas faced by clinical psychiatrists is considered generally and is illustrated by several case vignettes. Three case histories consider dementia vs depressive pseudodementia, two the possibility of a cerebral vasculitis in patients with auto-immune conditions, and two whether the patient had a "type" of depression likely to benefit from a course of ECT. Published studies reviewing the utility of SPECT in dementia, depression, depressive "pseudodementia" and cerebral lupus are considered. It is suggested that SPECT is an important investigatory technique providing additional information that may assist some diagnostic decisions, while its utility in assisting other clinical decisions awaits clarification.

The Korsakoff syndrome

BACKGROUND

Investigations of the Korsakoff syndrome by researchers from different disciplines have proliferated in recent years, making it apposite to review the various findings.

METHOD

This review is based on the author's knowledge of reports in the major clinical and neuropsychological journals, supplemented by Medline searches to update particular subtopics.

RESULTS

The Korsakoff syndrome is defined as a disproportionate impairment in memory, relative to other aspects of cognitive function, resulting from a nutritional (thiamine) depletion. The initial manifestations of the disorder are variable, and a persistent memory impairment can result from a non-alcoholic aetiology, although this seems to happen much less commonly than in the past - presumably because of generally higher standards of nutrition. Although there is agreement on the underlying neuropathology, the critical lesion sites for memory disorder have been debated. Recent evidence suggests that the circuit involving the mammillary bodies, the mammillo-thalamic tract and the anterior thalamus, rather than the medial dorsal nucleus of the thalamus, is particularly critical in the formation of new memories. The relationship of these deficits to thiamine depletion remains a topic of current investigation, as does the purported role of neurotransmitter depletions in the cholinergic, glutamate/GABA and catecholamine and serotonergic systems. Neuro-imaging studies have confirmed autopsy findings of more widespread structural and metabolic abnormalities, particularly involving the frontal lobes.

CONCLUSIONS

The relationship of these neuropathological, neurochemical, and metabolic abnormalities to cognitive functioning, with particular reference to specific aspects of memory processing, has been considered in some detail. Whereas structural and/or neurochemical abnormalities within the limbic/diencephalic circuits account for anterograde amnesia, some other factor, such as frontal lobe dysfunction, must underlie the severe retrograde memory loss which is characteristically found in this syndrome.

Decreased cingulate and precuneate glucose utilization in alcoholic Korsakoff's syndrome

Localized cerebral glucose utilization was determined for nine abstinent alcoholic men with Korsakoff's syndrome and 10 age-matched normal men who underwent positron emission tomography with [18F]2-fluoro-2-deoxyglucose (FDG). Patients with Korsakoff's syndrome showed relatively decreased glucose utilization in cingulate and precuneate areas. These decreases persisted even after correction for group differences in ventricular and sulcal cerebrospinal fluid measured on computed tomography. Electroencephalographic recordings at the time of FDG uptake showed no group differences, a finding that demonstrates that the metabolic differences could not be explained by differences in physiological arousal at the time of scanning. It is concluded that the decreased glucose utilization in the patients reflects a disruption of memory circuitry, the Papez circuit, caused by diencephalic lesions induced by thiamine deficiency.

Artificial neural networks that use single-photon emission tomography to identify patients with probable Alzheimer's disease

Single-photon emission tomographic (SPET) images using technetium-99m labelled hexamethyl-propylene amine oxime were obtained from 97 patients diagnosed as having Alzheimer's disease, as well as from a comparison group of 64 normal subjects. Multiple linear regression was used to predict subject type (Alzheimer's vs comparison) using scintillation counts from 14 different brain regions as predictors. These results were disappointing: the regression equation accounted for only 33.5% of the variance between subjects. However, the same data were also used to train parallel distributed processing (PDP) networks of different sizes to classify subjects. In general, the PDP networks accounted for substantially more (up to 95%) of the variance in the data, and in many instances were able to distinguish perfectly between the two subjects. These results suggest two conclusions. First, SPET images do provide sufficient information to distinguish patients with Alzheimer's disease from a normal comparison group. Second, to access this diagnostic information, it appears that one must take advantage of the ability of PDP networks to detect higher-order nonlinear relationships among the predictor variables.

Disorientation following stroke: frequency, course, and clinical correlates

To investigate the frequency, course, and clinical correlates of disorientation following stroke, we administered the Mini-Mental State Examination orientation subtest to 177 alert patients 7-10 days and 3 months after stroke and 240 stroke-free nondemented subjects. Disorientation was defined as a score < or = 8/10. Seventy-two (40.7%) of the patients were disoriented 7-10 days after stroke and 39 patients (22.0% of the sample) remained disoriented 3 months later. A logistic regression analysis determined that persistent disorientation was significantly related to stroke status [odds ratio (OR) = 5.8], after adjusting for memory and attentional deficits and demographic variables. Among stroke patients, disorientation was associated with severe hemispheral stroke syndromes (OR = 7.7), but not infarct location or vascular risk factor history, after adjusting for memory and attentional deficits and demographic variables. Sensitivity and specificity analyses determined that disorientation was an inaccurate marker for dementia or deficits in memory or attention, while intact orientation was associated with a low probability of dementia or memory dysfunction in most patients but not preserved attention. We conclude that disorientation is common and persistent following stroke and associated with severe hemispheral stroke syndromes but not infarct location. While disorientation is a poor marker for dementia or deficits in memory or attention, intact orientation should suggest that cognitive functions are likely to be preserved.

Uptake of 99mTc-exametazime shown by single photon emission computerized tomography in obsessive-compulsive disorder compared with major depression and normal controls

Twelve patients with obsessive-compulsive disorder (OCD) were investigated at rest using single photon emission computerized tomography with 99mTc-exametazime. The uptake of 99mTc-exametazime was expressed relative to calcarine/occipital cortex. Patients were matched for drug treatment with 12 patients with a major depressive episode and the patient groups were compared with a control group. Significant bilateral decreases in tracer uptake were confined to basal ganglia in the OCD group. There was a paradoxical positive correlation between anxiety ratings and tracer uptake to basal ganglia in the OCD group. The findings confirm that the functional topography of OCD implicates altered function in the basal ganglia.

PASAT performance and the pattern of uptake of 99mTc-exametazime in brain estimated with single photon emission tomography

The effect of the paced auditory serial addition test (PASAT) on the regional uptake of 99mTc-exametazime was determined by single photon emission computed tomography. Twenty insulin-treated diabetic outpatients were scanned at rest and during the performance of the PASAT task using split-dose injection of tracer. When resting and activation scans were compared there were significant decreases in tracer uptake in the right anterior cingulate and left posterior cingulate areas during PASAT activation. The findings are compared with previous studies which had implicated the anterior cingulate area in the mechanisms of attention in humans and other animals. The potentially confounding role of anxiety during attentional tasks is discussed.

Heterogeneity of neocortical cerebral blood flow deficits in dementia of the Alzheimer type: a [99mTc]-d,l-HMPAO SPECT study

Regional cerebral blood flow (rCBF) was measured with high resolution brain dedicated single photon emission computer tomography (SPECT) and [99mTc]-d,l-hexamethyl-propylene-amine-oxime (HMPAO) in 25 patients with probable Alzheimer's disease and in 25 control subjects, selected according to rigorous inclusion and exclusion criteria. The aim was to analyse the topography of rCBF deficits in individual patients. In the group of patients with Alzheimer's disease as a whole, global CBF was reduced, but a factorial analysis of variance did not show disproportionate reduction of rCBF in any brain region. A parametric analysis of the rCBF data in individual patients was carried out with reference to normal values for internal rCBF ratios and to 13 different abnormal rCBF patterns. These theoretical patterns were predefined by showing significant hypoperfusion in at least one, or in any relevant combination of two, three, or four, of four major brain regions (a left and right frontal and a left and right posterior region). All patients with Alzheimer's disease and none of the control subjects had an abnormal rCBF pattern. Eleven of the 13 different patterns were seen in the patients. Frontal changes were seen in 19 (76%) of the patients, more often than previously reported. No single Alzheimer's disease pattern could be derived from our data. The number of regions with hypoperfusion, but not the presence of frontal changes, correlated significantly with the duration of disease. It is concluded that a clinical diagnosis of probable Alzheimer's disease is associated with heterogeneous patterns of rCBF deficits as measured with SPECT and [99mTc]-d,l-HMPAO. This heterogeneity may reflect different stages of the disease or cognitive subtypes and help explain published discrepancies concerning the topography of hypoperfusion in Alzheimer's disease. An analysis of individual rCBF data may add important information in the investigation of diseases with heterogeneous effects on the brain.

Memory impairment in schizophrenia--a comparison with that observed in the Alcoholic Korsakoff syndrome

Until very recently, memory impairment was not considered to be a central feature of schizophrenia, except in chronic, deteriorated patients. In this study of a heterogeneous sample of 40 patients with DSM-III-R schizophrenia, episodic memory impairment was found to be prevalent, and in some cases, severe. The degree of memory impairment was not attributable to neuroleptic or anticholinergic medication, or to poor motivation or cooperation. These results, therefore, replicate those reported by McKenna et al. (1990) and Tamlyn et al. (1992), who suggested that the pattern of memory impairment in schizophrenia may conform in important respects to that of the classic amnesic syndrome. However, in a direct comparison of the schizophrenic sample with 18 patients suffering from the Alcoholic Korsakoff Syndrome (AKS), both quantitative and qualitative differences were found to exist between the two groups of patients. In particular, the level of long-term episodic memory impairment was found in the AKS sample to be far greater than that in the schizophrenic group. An interesting possible double-dissociation emerged between the two groups; although demonstrating superior episodic memory functioning, the schizophrenic sample were found to perform significantly more poorly than the AKS sample on a test of semantic memory.

Clonidine infusion increases uptake of 99mTc-Exametazime in anterior cingulate cortex in Korsakoff's psychosis

The effects upon regional brain function of infusing either saline or clonidine (1.5 microgram/kg) has been examined in 18 patients with alcoholic Korsakoff's psychosis using 99mTc-hexamethylpropyleneamineoxime (99mTc-HMPAO or 99mTc-Exametazime) and Single Photon Emission Tomography (SPET or SPECT). The hypothesis tested was that frontal lobe function would be increased by adrenoceptor stimulation. This was confirmed by an increase in the uptake of 99mTc-Exametazime into anterior cingulate regions of the frontal lobes. Patients were scanned before and after saline or clonidine infusion during performance of a verbal fluency task. There was a significantly increased performance of verbal fluency in patients given clonidine. This effect was variable and could not be unequivocably distinguished from increases in performance in the saline treated group. Nevertheless, the increase in neuropsychological performance was also correlated with increased function in left dorsolateral frontal cortex within the clonidine treated group. An exploratory examination of other brain areas suggested that relative increases in posterior cingulate cortex and changes in the symmetry of function within the thalamus may also be produced by acute infusion of clonidine in Korsakoff patients. The findings support the idea that adrenergic mechanisms may modulate cognitive performance by actions on attentional systems within the brain. These appear to be located primarily within limbic cortex. It is, of course, notable that this can occur in patients with profound and disabling amnesia.

Single photon emission computerised tomography in elderly patients with Alzheimer's disease and multi-infarct dementia. Regional uptake of technetium-labelled HMPAO related to clinical measurements

Single photon emission computerised tomography (SPECT) was used to measure regional brain uptake of technetium-99m hexamethylpropyleneamine oxine (Tc99m-HMPAO) in elderly patients with Alzheimer's disease (AD), multi-infarct dementia (MID) and normals (n = 20 in each group). Different patterns of uptake were found between groups when cortical uptake was normalised to cerebellar uptake. Reductions occurred in all regions in AD, being most marked in temporal and posterior parietal areas. Significant correlations were found in AD between memory impairment and decreased temporal uptake bilaterally, and between duration of illness and reduced uptake in most brain regions. MID patients showed higher uptake in the anterior parietal region than did the other groups. A variable comparing anterior to posterior uptake significantly discriminated the two patient groups.

A single photon emission computerised tomography study of regional brain function in elderly patients with major depression and with Alzheimer-type dementia

The uptake, at rest, of 99mTc-exametazime into different brain regions was compared using SPECT for 20 elderly subjects with major depressive disorder, 20 with Alzheimer-type dementia, and 30 age-matched normal volunteers. Uptake was referred to calcarine-occipital cortex as a reference sensory area. Cross-sectional differences between the three groups were highly statistically significant, but reflected primarily the reductions in cortical uptake in the Alzheimer group. A detailed comparison of depressed patients and controls identified decrements in anterior cingulate, temporal and frontal cortex and in caudate and thalamus in men only. These decrements were correlated with impairment of performance on a trail-making task, but were also associated with continuing treatment with antidepressants or benzodiazepines. However, most depressed patients had quantitatively normal scans for posterior parietal association cortex, and this suggests that SPECT may find a limited role in the differential diagnosis of depression and dementia. The reduced brain function in some depressed patients may parallel the findings from studies of brain structure in elderly depressives; there was between good outcome at 6-18 months and increased tracer uptake in subcortical areas.

A single photon emission computerised tomography study of regional brain function underlying verbal memory in patients with Alzheimer-type dementia

Ten patients with Alzheimer-type dementia and nine age-matched normal controls were examined with SPECT, using split-dose 99mTc-labelled exametazime. The baseline condition involved repetition of the word 'yes' or 'no'. The activation condition involved recognition (indicated by a 'yes' or 'no') of words from a previously learned list presented along with distractor words. Patients who performed this task successfully were selected, and efforts were made to match the patients with controls according to their performance on the task, although this was not fully achieved. Uptake of 99mTc-exametazime was estimated at baseline and during the word-recognition task for predetermined regions of interest drawn from a standard neuroanatomical atlas. The baseline task appeared to normalise tracer uptake for frontal, temporal and parietal cortex in the patient group. However, during the recognition task, controls but not patients showed activation effects. These were most prominent in dorsolateral frontal cortex and adjacent anterior cingulate cortex. Among patients, successful performance was correlated with activation of dorsolateral frontal and parietal cortex on the left side. The results confirm the central role of frontal mechanisms in a recognition memory task. The study highlights some of the difficulties of using cognitive challenge tests in clinical groups.

The pattern of regional cerebral blood flow during alcohol withdrawal--a single photon emission tomography study with 99mTc-HMPAO

Cerebral blood flow was investigated during alcohol withdrawal in 15 male alcoholics by single photon emission computerized tomography with 99mTc-HMPAO and compared with the results of a second study 3 weeks later when all symptoms of withdrawal had disappeared and when the patients had been free of medication for at least 1 week. Slice images were reconstructed parallel to the orbitomeatal plane, and tracer activity was analyzed in 8 regions of interest per hemisphere. During alcohol withdrawal a special pattern of cerebral blood flow distribution could be observed. Relative perfusion was elevated in both inferior temporal regions, whereas it was reduced in the superior temporal region of both hemispheres. The changes of cerebral blood flow distribution did not correlate with neuropsychological findings nor with the severity of withdrawal syndrome.

Abnormalities in rCBF and computed tomography in patients with Alzheimer's disease and in controls

The pattern of abnormal distribution of the single photon emission computed tomography (SPECT) cerebral blood flow tracer 99m-technetium-hexamethylpropyleneamine oxime (99Tcm-HMPAO) was investigated in 14 patients with clinically diagnosed Alzheimer's disease (AD) who subsequently had post-mortem confirmation of the disease and also in 14 elderly control subjects. These abnormalities were compared with computed tomography (CT) scans to investigate the degree to which the focal SPECT deficits were due to atrophy. The results show that SPECT imaging with 99Tcm-HMPAO and CT scanning both have a higher incidence of abnormality in AD patients than in controls and that the difference between patients and controls is greater with SPECT than with CT. Frontal SPECT and CT abnormalities in moderate/severe Alzheimer's disease occur as frequently as temporal/occipital abnormalities but the latter are rare in control subjects. Around 50% of the SPECT deficits occur in CT normal brain regions, showing that atrophy is not the sole cause of SPECT deficits.

A study of regional cerebral blood flow and cognitive performance in Alzheimer's disease

Thirty five patients with dementia of the Alzheimer type (DAT) and 35 controls matched for age, sex and handedness were investigated using single photon emission computer tomography (SPECT) with 99m technetium HMPAO. Regional cerebral blood flow (rCBF) was assessed semi-quantitatively in 18 cortical and 4 subcortical areas by normalising mean information density in each region to cerebellar mean information density. Analysis revealed significantly reduced rCBF to temporal, parietal, frontal and left occipital cortex in the patients whilst blood flow to subcortical areas showed no differences between the 2 groups. In addition, significant left-sided cortical hypoperfusion was seen in the DAT group but not in controls. When patients were sub-divided on the basis of disease severity, those with mild disease showed temporal, parietal and left frontal changes with more severely affected patients also showing right frontal and left occipital involvement. rCBF patterns did not distinguish between presenile and senile onset cases once duration and severity of illness were controlled. Eight cortical areas were also rated visually for perfusion deficits on a simple 4 point scale. Perfusion deficits were detected in 34 of 35 patients but in only 4 of 35 controls. In the DAT group significant correlations were found between many of the neuropsychological tests used and rCBF. Memory correlated with left temporal activity, praxis, perception, object assembly and block design with right parietal activity and language with activity throughout the left hemisphere. Significant correlations were also seen between subcortical and cortical blood flow, possibly explaining the correlations observed between many of the neuropsychological tests and thalamic blood flow.