Event-related potentials of episodic encoding after traumatic brain injury in older adults.

Episodic memory and attention impairments are frequently observed following a traumatic brain injury (TBI). Older adults are more affected than young adults after a TBI, partly because of the age-related neural and memory changes. Neural mechanisms underlying episodic memory deficits in older adults with chronic TBI remain to be investigated. The current study aimed to investigate the impact of TBI in older adults on the neural mechanisms of episodic encoding. Event-related potentials were recorded while 13 participants with mild-to-severe TBI and 14 matched controls were performing an episodic memory task in which the level of organizational strategy was manipulated through three encoding conditions. Participants were explicitly instructed to memorize words without any semantic relationship (Unrelated condition), words semantically related without any given strategies (Spontaneous condition) and words semantically related with provided category labels and organizational strategy (Guided condition). Behavioral performances indicated that older individuals with a TBI were impaired compared to matched controls whatever the condition. The electrophysiological findings showed a reduction of the P200 and LPC components amplitude in the TBI group relative to control group. Moreover, control participants without any neurological history showed a right frontal sustained activity only in the Spontaneous condition, whereas a right frontal asymmetry was observed in participants with chronic TBI whatever the encoding conditions. This was mainly the result of negative left frontal activity. These findings evidence neural dysfunctions underlying attentional and associative processes involved in memory strategies after a TBI sustained at an older age that are consistent with executive functions impairments.