Neuroscience Letters 385 (2005) 114–119 Differential amygdala habituation to neutral faces in young and elderly adults Michelle M. Wedig a , Scott L. Rauch a , Marilyn S. Albert b , Christopher I. Wright a,b,c,∗ a Psychiatric NeuroimagingResearch Program, Massachusetts General Hospital, Harvard Medical School, 13th Street, Building 149, 2nd Floor, Charlestown, MA 02129, USA b Gerontology Research Unit, Massachusetts General Hospital, Harvard Medical School, 13th Street, Building 149, 2nd Floor, Charlestown, MA 02129, USA c Brigham Behavioral Neurology Group, Department of Neurology, Brigham and Women’s Hospital, Boston, MA 02115, USA Received 10 January 2005; received in revised form 16 May 2005; accepted 16 May 2005 Abstract Habituation is a highly adaptive property of the nervous system, which allows for the allocation of attention and other cognitive resources to more imperative environmental events. The amygdala is an important site of habituation in humans, but no studies to date have examined the effects of aging on amygdala habituation. Given the amygdala’s role in evaluating the salience of a stimulus and initiating behavioral responses, the potential importance of amygdala habituation in aging may be far-reaching. Therefore, we assessed for differences in habituation in the amygdalae of healthy young and elderly adults during repeated presentations of neutral human faces using functional magnetic resonance imaging (fMRI). In addition, we evaluated the relationship between amygdala volume and habituation, to examine the effects of atrophy. Eighteen healthy young controls and 18 healthy elderly subjects were scanned with fMRI during viewing of repeatedly presented neutral human face stimuli. Significant fMRI signal decrement was observed across all subjects for early versus late face presentations. Analysis of group, condition, and hemisphere revealed a significant three-way interaction, with right greater than left habituation in the young, but left greater than right amygdala habituation in the elderly. Volumetric and correlational analyses demonstrated that amygdala volume is associated with habituation in the right, but not left, hemisphere. We conclude that, in healthy elderly adults, the amygdala retains its adaptive habituation response, but speculate that intrinsic changes in amygdala anatomy during aging may modulate its laterality. © 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: Magnetic resonance imaging; Amygdala; Habituation; Aging Habituation, or a decrement of response to repeatedly pre- sented stimuli, has been described as an adaptive property of the nervous system that evolved for ignoring sensory input no longer of current relevance to an organism. This process allows for the allocation of attention and other cog- nitive resources to more imperative environmental events, and is evident throughout the animal kingdom from aplysia to humans [20]. Although the prefrontal cortex plays an inte- gral part in the allocation of attention in humans [20], the amygdala is also essential in evaluating stimulus salience and initiating behavioral responses based on the initial assess- ment of the present stimulus. In this regard, previous studies ∗ Corresponding author. Tel.: +1 617 724 2324; fax: +1 617 726 4078. E-mail address: ciwright@partners.org (C.I. Wright). have shown rapid amygdala habituation to repeatedly pre- sented complex visual stimuli, including neutral and emo- tional human faces [2,7,8,18,19,23]. Several works have also demonstrated some hemispheric laterality to this phe- nomenon, with greater habituation in the right versus the left amygdala depending on the combination of stimuli used in those studies [2,7,8,18,23]. Most investigations of habitua- tion have, however, focused on healthy young adults, and the few studies on habituation in the elderly have not examined the role of the amygdala. For example, galvanic skin response (GSR) to both a tone [4] and a shock [5] has been shown to habituate more slowly in older adults compared to younger ones. Likewise, an evoked potentials study [10] found a lack of novelty P3 habituation in the elderly as compared to young participants. In contrast, 0304-3940/$ – see front matter © 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2005.05.039