Magnetic resonance imaging (MRI) of the hippocampus has been extensively studied on neurological and psychiatric disorders. Particularly in studies on schizophrenia and mood disorders, findings regarding the hippocampal involvement have been most controversial. Previously, minor volume loss of the hippocampus in alcoholism, a major comorbidity alongside psychiatric disorders, has been reported.

No data has existed on the hippocampal volumes in subtypes of alcoholism, despite the need and interest to further identify and study subgroups of alcoholics with psychiatric and behavioral syndromes that occur outside and within the context of their abuse. In this case, the distinction was drawn to alcoholism with and without antisocial and violent behavior.

In the first of the two studies, MRI was used to measure volumes of the hippocampus in late-onset type 1 alcoholics and early-onset type 2 alcoholics.

Of these, the type 1 alcoholism is typically characterized to represent late-onset alcoholism with substantially preserved social and occupational behavior, and relatively intact impulse control. These subjects are typically characterized as anxiety-prone personalities, typically with the alcoholism consisting of alternating periods of binges and abstinence. The type 1 alcoholics were recruited from a local rehabilitation center.

In contrast, the type 2 alcoholics represent early-onset alcoholism, and their behavior is characterized by euphoria-seeking personality which is typically associated with impulsive, criminal, antisocial and violent behavior. The type 2 alcoholic subjects were also violent offenders with antisocial personality disorder, derived from a forensic psychiatric sample. All had a history of violent episodes, several of them were in custody because of homicide, but all were diagnosed non-psychotic and legally competent.

Compared to the controls, the right hippocampal volumes were significantly smaller in both alcoholic groups. While there was no correlation between the hippocampal volumes with age in the control subjects, there was tendency towards decreased volumes with aging and also with the duration of alcoholism in the type 1 alcoholic subjects. This suggests that alcoholism without major psychiatric or other comorbidities is associated with decline in hippocampal volumes. On the contrary, there was a significant positive correlation between the right hippocampal volume and age and duration of alcoholism in the type 2 alcoholics.

Because the study was cross-sectional, it would be premature to conclude that alcohol and polysubstance abuse, violence, and antisocial lifestyle would actually increase the hippocampal volumes, other alternatives had to be sought.

From the introduction of the type 1 versus 2 dichotomy the question has remained whether the type 2 category is representative of primary alcoholism or only secondary or symptomatic to an underlying antisocial personality disorder. These effects suggest that there are profound biological differences between the two alcoholic groups, and raise the possibility that the observed effects within the type 2 category are due to other factors than the cumulative acquired effects related to alcohol abuse, such as primary personality psychopathology.

The study thus provides further evidence that type 1 alcoholism, in general, is associated with a minor loss in hippocampal volume. It is also suggested that type 2 alcoholism, in general, similarly displays a minor decrease in hippocampal volume, but this decrease is unevenly distributed within the type 2 category, being weighted towards the younger subjects.

The possibility that differences in degree of psychopathy would explain the findings in the type 2 alcoholics - the positive correlation between the hippocampal volumes and age - was studied in a the latter of the studies. It was hypothesized that subjects in their early twenties would be likely to display higher degree of psychopathy, being natural born killers, delinquente nato, than those who are being examined in their forties in forensic psychiatric evaluation due to violent offending.

The degree of subjects' psychopathy was studied using the Psychopathy Checklist - Revised (PCL-R) and an inverse correlation was found - the smaller the hippocampi, the more severe the degree of psychopathy. The strongest correlations were found in the posterior hippocampus. The posterior hippocampus is know to participate in processes, such as conditioning and forming associations. This is the first study to date to find structure-function (or structure-malfunction) correlation in terms of degree of psychopathy.

A prototypical psychopath may be impoverished in conditioning, which may be the simplest form of association process. To put it in a nutshell, a prototypical psychopath may not learn from making mistakes. Wrong-doing in psychopath does not activate [autonomic] mechanisms that would say "if you do this [harm to others], that [punishment] follows". The hippocampus may thus play a crucial learn in socialization, or as is the case in psychopaths, lack thereof.

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Source:

Laakso MP, Vaurio O, Savolainen L, Repo E, Soininen H, Aronen HJ, Tiihonen J. A volumetric MRI study of the hippocampus in type 1 and 2 alcoholism. Behav Brain Res 2000;109:177-186

Laakso MP, Vaurio O, Koivisto E, Savolainen L, Eronen M, Aronen HJ, Hakola P, Repo E, Soininen H, Tiihonen J. Psychopathy and the posterior hippocampus. Behav Brain Res 2001;118: 187-193

Correspondence:

Mikko Laakso
Department of Neurology
Bldg. 5
Kuopio University Hospital
POB 1777
70211 Kuopio
Finland

E-mail: mikko.laakso@uku.fi