Behavioural Brain Research 118 (2001) 187 – 193 Research report Psychopathy and the posterior hippocampus Mikko P. Laakso a,b, *, Olli Vaurio c , Esa Koivisto d , Liisa Savolainen c , Markku Eronen c,d , Hannu J. Aronen b , Panu Hakola c , Eila Repo c , Hilkka Soininen a,e , Jari Tiihonen c,f a Department of Neurology, Bldg. 5, Kuopio Uniersity Hospital, POB 1777, 70211, Kuopio, Finland b Department of Clinical Radiology, Kuopio Uniersity Hospital, POB 1777, 70211, Kuopio, Finland c Department of Forensic Psychiatry, Uniersity of Kuopio, Niuanniemi Hospital, 70240, Kuopio, Finland d Vanha Vaasa Hospital, POB 13, 65381, Vaasa, Finland e Department of Neuroscience and Neurology, Uniersity of Kuopio, POB 1627, 70211, Kuopio, Finland f Department of Clinical Physiology, Kuopio Uniersity Hospital, POB 1777, 70211, Kuopio, Finland Received 14 April 2000; received in revised form 6 September 2000; accepted 7 September 2000 Abstract Neurobiology of psychopathy is of interest, not only because neural underpinnings of psychopathy remain obscure, but also because psychopaths may provide a model to study violent behavior, neurology of morals and impaired decision-making. Medial temporal lobe pathology has been suggested to be a part of the neural systems dysfunction which manifests as violent and psychopathic behavior. Yet, so far no sound evidence of neuroanatomical correlates for psychopathic behavior has been found. In this study regional hippocampal volumes were measured using magnetic resonance imaging in 18 habitually violent offenders with antisocial personality disorder and type 2 alcoholism (derived from forensic psychiatric evaluation). The regional volumes along the anteroposterior axis of the hippocampus were correlated with the subjects’ degree of psychopathy as evaluated by the Psyhopathy Checklist-Revised. Strong negative correlations, up to -0.79, were observed, among the study subjects, between the psychopathy scores and the posterior half of the hippocampi bilaterally. These data are in accordance with experimental studies proposing that lesions of the dorsal hippocampus impair acquisition of conditioned fear, and with theories on psychopathology according to which one of the central features in the birth of psychopathy is a deficit in acquisition of conditioned fear. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Aggression; Behavior; Human; Psychopathy; Sociopathy; Violence www.elsevier.com/locate/bbr 1. Introduction Neurology of morals and social cognition, i.e. pro- cesses that subserve complex social behaviors, which remains largely unknown, has recently received much deserved attention [1,9]. Yet, to date studies on impair- ment of social behavior have been conducted mainly on subjects with autism [12,26,30] or on a small number of individuals with isolated lesions of the ventromedial prefrontal cortex (PFC), which are known to impair decision-making. Studies on a few subjects with early onset lesions of the ventromedial PFC have proposed that lesions at an early age additionally impair moral and social reasoning and lead to antisocial behavior [2,27]. Compared with autism or a few subjects with isolated brain damage, there is a group of subjects that constantly violate social norms, display inflexible be- havioral patterns and inability to feel remorse or learn from experience, and who harm themselves and others in the process of their behavior, namely the develop- mental sociopaths or psychopaths [8]. The birth of psychopathy and violence is dependent on factors related with culture, nurture, and biology. Yet, no matter what the culture or how good the * Corresponding author. Tel.: +358-17-173015; fax: +358-17- 173019. E-mail address: mikko.laakso@uku.fi (M.P. Laakso). 0166-4328/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0166-4328(00)00324-7