Brain imaging in alcoholism

The contribution of mamillary body damage to Wernicke's encephalopathy and Korsakoff's syndrome

Histopathological alterations of the mamillary bodies are the most conspicuous and the most consistent neuropathological features of several disorders that occur after severe thiamine deficiency, such as Wernicke's encephalopathy and Korsakoff's syndrome. Moreover, they are among the few abnormalities that are visible to the naked eye in these disorders. With a lifetime prevalence of approximately 1.3%, Wernicke's encephalopathy is by far the most frequent cause of damage to the mamillary bodies in humans. Still, there is a persisting uncertainty with regard to the development and the clinical consequences of this damage, because it is virtually impossible to study in isolation. As a rule, it always occurs alongside neuropathology in other subcortical gray matter structures, notably the medial thalamus. Converging evidence from other pathologies and animal experiments is needed to assess the clinical impact of mamillary body damage and to determine which functions can be attributed to these structures in healthy subjects. In this chapter, we describe the history and the current state of knowledge with regard to thiamine deficiency disorders and the contribution of mamillary body damage to their clinical presentations.

Neural reward and punishment sensitivity in cigarette smokers

BACKGROUND

Nicotine addiction remains a major public health problem but the neural substrates of addictive behavior remain unknown. One characteristic of smoking behavior is impulsive choice, selecting the immediate reward of smoking despite the potential long-term negative consequences. This suggests that drug users, including cigarette smokers, may be more sensitive to rewards and less sensitive to punishment.

METHODS

We used event-related potentials (ERPs) to test the hypothesis that smokers are more responsive to reward signals and less responsive to punishment, potentially predisposing them to risky behavior. We conducted two experiments, one using a reward prediction design to elicit a Medial Frontal Negativity (MFN) and one using a reward- and punishment-motivated flanker task to elicit an Error Related Negativity (ERN), ERP components thought to index activity in the cortical projection of the dopaminergic reward system.

RESULTS AND CONCLUSIONS

The smokers had a greater MFN response to unpredicted rewards, and non-smokers, but not smokers, had a larger ERN on punishment motivated trials indicating that smokers are more reward sensitive and less punishment sensitive than nonsmokers, overestimating the appetitive value and underestimating aversive outcomes of stimuli and actions.

Diffusion-weighted magnetic resonance imaging in Marchiafava–Bignami disease: follow-up studies

Marchiafava-Bignami disease (MBD), an acute toxic demyelination of the corpus callosum in alcoholics, is associated with poor evolution in the majority of patients. We report here the early and late diffusion magnetic resonance imaging (MRI) and apparent diffusion coefficient (ADC) studies of two patients suffering from MBD with favourable outcome. Diffusion and anatomical MRI changes were parallel to the clinical evolution, suggesting that MRI studies can be helpful for diagnosis and follow-up. Unlike in stroke, restricted diffusion on ADC maps does not seem to be a sign of irreversibility.

Marchiafava-Bignami disease: two cases with favourable outcome

Marchiafava-Bignami disease (MBD) is a rare disorder of an unknown aetiology but strongly associated with alcoholism. MBD primarily affects the corpus callosum leading to confusion, dysarthria, seizures and frequently to death. Over 250 cases from all races and from almost all nationalities have been reported, most cases being alcoholics. We report two cases with a favourable outcome. Magnetic resonance imaging (MRI) demonstrated a typical lesion of the corpus callosum, in both patients. The patients, a 44-year-old male and a 40-year-old female, presented with depressed consciousness and a variety of other symptoms, but finally made a reasonably good recovery leading to home discharge. To the best of our knowledge, only one additional case of MBD from Scandinavia has been published. As alcoholism is a major public health problem in Scandinavia, we assume that MBD is underdiagnosed and/or under-reported. Non-specific general symptoms and encephalopathy in an alcoholic may harbour undiagnosed MBD. We suggest that the incidence of MBD may be higher and its prognosis may be milder than generally believed.

Brain correlates of memory dysfunction in alcoholic Korsakoff's syndrome

OBJECTIVES

To investigate the relation between anterograde amnesia and atrophy of brain structures involved in memory processing in alcoholic Korsakoff's syndrome.

METHODS

The volume of brain structures involved in memory processing was measured with MRI from 13 subjects with Korsakoff's syndrome, 13 subjects with chronic alcoholism without Korsakoff's syndrome, and 13 control subjects. The brain structures analysed were the hippocampus, the parahippocampal gyrus, the mamillary bodies, the third ventricle, and the thalamus. Brain volumes were correlated with the delayed recall of a verbal learning test.

RESULTS

Compared with subjects with chronic alcoholism and control subjects, subjects with Korsakoff's syndrome had a reduced volume of the hippocampus, the mamillary bodies, and the thalamus, and enlargement of the third ventricle. The impairment of delayed recall correlated with the volume of the third ventricle (r=-0.55, p=0.05) in the Korsakoff group.

CONCLUSIONS

Anterograde amnesia in alcoholic Korsakoff's syndrome is associated with atrophy of the nuclei in the midline of the thalamus, but not with atrophy of the mamillary bodies, the hippocampus, or the parahippocampal gyrus.