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It has been suggested previously that patients with a frontal lobe lesion might have a specific impairment in the retrieval of the source of information despite adequate memory for facts. Patients with an anterior temporal excision are known to have impairments in memory for facts and the question arises as to whether they are also impaired in source memory. The present study compared memory for facts and their source in patients with a unilateral frontal cortical or an anterior temporal excision in a situation in which both types of information were encoded explicitly. Patients with a unilateral frontal cortex or a temporal lobe excision watched videos of a game show and were instructed to attend to both the trivia facts and their source (the identity of the speaker or the relative time of presentation). Patients with a frontal cortex excision were not impaired on either fact or source memory. This was true even when a subgroup of patients with an excision involving the dorsolateral frontal cortex was examined. In contrast, patients with a left temporal lobe excision were impaired in both fact and identity source memory and right temporal lobe patients were impaired in identity source memory. All patients performed similarly to normal controls in temporal source memory. The present results are consistent with the view that source information is part of an associative network of information about an episode and that the medial temporal region is critical for both source and content memory. Furthermore, if source information is encoded explicitly, the frontal cortex does not appear to be necessary for its retrieval. Instead, it is proposed that the frontal cortex plays a metacognitive role in memory retrieval.

Previous research has raised questions regarding the necessity of the frontal cortex in autobiographical memory and the role that it plays in actively retrieving contextual information associated with personally relevant events. Autobiographical memory was studied in patients with unilateral excisions restricted to the frontal cortex or temporal lobe involving the amygdalo-hippocampal region and in normal controls using an event-sampling method. We examined accuracy of free recall, use of strategies during retrieval and memory for specific aspects of the autobiographical events, including temporal order. Patients with temporal lobe excisions were impaired in autobiographical recall. By contrast, patients with frontal cortical excisions exhibited normal autobiographical recall but were less likely to use temporal order spontaneously to organize event retrieval. Instruction to organize retrieval by temporal order failed to improve recall in temporal lobe patients and increased the incidence of plausible intrusion errors in left temporal patients. In contrast, patients with frontal cortical excisions now surpassed control subjects in recall of autobiographical events. Furthermore, the retrieval accuracy for the temporal order of diary events was not impaired in these patients. In a subsequent cued recall test, temporal lobe patients were impaired in their memory for the details of the diary events and their context. In conclusion, a basic impairment in autobiographical memory (including memory for temporal context) results from damage to the temporal lobe and not the frontal cortex. Patients with frontal excisions fail to use organizational strategies spontaneously to aid retrieval but can use these effectively if instructed to do so.

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