Abnormalities of the Hippocampus in Sudden and Unexpected Death in Early Life

Abstract

The terrifying aspect of the sudden infant death syndrome (SIDS) is that it occurs in infants who seem healthy and then die without warning when put down to sleep. SIDS is not typically witnessed and it is surmized that death occurs during sleep, or during one of the many transitions to waking that occur during normal infant sleep-wake cycles (1). Multiple sleep-related mechanisms have been proposed to cause SIDS (1, 2). These mechanisms include suffocation/asphyxiation in the face-down sleep position, central and/or obstructive sleep apnea, impaired-state-dependent responses to hypoxia and/or hypercarbia, inadequate autoresuscitation, defective autonomic regulation of blood pressure or thermal responses, and abnormal arousal to life-threatening challenges during sleep.In this chapter, we review the hypothesis and the neuropathologic evidence that SIDS is precipitated by a dentate gyrus-related seizure or a limbic-related instability that involves the central homeostatic network (CHN). We begin with an overview of this hypothesis, and then review our neuropathologic evidence for an epileptiform hippocampal lesion in the brain of a subset of SIDS infants and young children (41-50% respectively) who died suddenly and unexpectedly (3-5). We then consider the putative mechanism whereby dentate lesions cause seizures, the role of the hippocampus as part of the CHN in stress responses (such as the face-down sleep position), and the potential interactions of brainstem serotonergic (5-HT) deficits and the hippocampus in the pathogenesis of sudden death in infants. We conclude with further directions for research into the role of the hippocampus in sudden and unexpected death in early life.