Abstract
Developmental amnesia (DA) is a selective episodic memory disorder associated with hypoxia-induced bilateral hippocampal atrophy of early onset. Despite the systemic impact of hypoxia-ischaemia, the resulting brain damage was previously reported to be largely limited to the hippocampus. However, the thalamus and the mammillary bodies are parts of the hippocampal-diencephalic network and are therefore also at risk of injury following hypoxic-ischaemic events. Here, we report a neuroimaging investigation of diencephalic damage in a group of 18 patients with DA (age range 11–35 years), and an equal number of controls. Importantly, we uncovered a marked degree of atrophy in the mammillary bodies in two thirds of our patients. In addition, as a group, patients had mildly reduced thalamic volumes. The size of the anterior-mid thalamic (AMT) segment was correlated with patients' visual memory performance. Thus, in addition to the hippocampus, the diencephalic structures also appear to play a role in the patients' memory deficit.
Highlights
Situated within the medial-temporal lobe, the hippocampus is vulnerable to damage during hypoxic-ischaemic episodes due to its high oxygen requirement and susceptibility to glutamate-induced neurotoxicity (Schmidt-Kastner & Freund, 1991)
We reported a causal sequence from exposure to neonatal hypoxia-ischaemia leading to significant hippocampal pathology, in turn resulting in a pronounced deficit in episodic recall in the absence of deficits in semantic memory, working memory, academic attainments and intelligence
In patients with amnesia resulting from hypoxicischaemic events, the hippocampus is the structure predicted to exhibit the largest degree of atrophy
Summary
Situated within the medial-temporal lobe, the hippocampus is vulnerable to damage during hypoxic-ischaemic episodes due to its high oxygen requirement and susceptibility to glutamate-induced neurotoxicity (Schmidt-Kastner & Freund, 1991) These systemic events are associated with a cascade of direct and secondary neuropathology (Faro & Windle, 1969) affecting multiple brain regions Caine and Watson's (2000) survey of neuropathological studies revealed that the thalamus was affected in 56% of anoxic patients In addition to these direct effects, the mammillary bodies and nuclei of the thalamus can become damaged after injury to the hippocampus by anterograde degeneration (Bachevalier & Meunier, 1996). Hippocampal injury is known to produce degeneration of both the mammillary bodies (Loftus, Knight, & Amaral, 2000; Schubert & Friede, 1979) and the thalamus (Kodama et al, 2003)
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