Event-related potential evidence for a specific recognition memory deficit in adult survivors of cerebral hypoxia.

Transient global ischaemia due to cardiac arrest may lead to profound neuropsychological disorders. Recent research indicates that memory processes are particularly impaired after hypoxic brain injury. Visual recognition memory functions were examined in these patients by means of event-related potential (ERP) and performance data. Eight chronic hypoxic patients, matched with controls for sex and age, performed a visual recognition memory task requiring recognition judgements for either object forms or spatial locations and a visual classification (i.e. oddball) task that imposed negligible memory demands. Reliable P300 oddball effects were obtained both for patients and for controls, whereas the two groups differed in P300 latency and P300 scalp topography. In the memory task, old/new effects (i.e. larger ERP waveforms for previously studied than for unstudied items) were found for the controls. In contrast, in patients these old/new effects were absent or even inverted in polarity while recognition performance was well above chance level, except for one patient. These results suggest that recognition, based on the retrieval of an item's study episode, is degraded in patients who have suffered a period of transient global ischaemia. In the light of the patients' above-chance level of recognition performance and the outcome of post hoc analysis of practice-related changes in recognition performance, it is argued that the patients' memory disorders are best characterized as a degradation of explicit memory functions such as episodic retrieval of a study episode. Implicit functions such as cognitive skill learning were intact.