Dissociation between verbal and autonomic measures of memory following frontal lobe damage

Objective: The objective of this study was to contrast overt verbal versus covert autonomic responses to facial stimuli in a patient with false recognition following frontal lobe damage. Background: False recognition has been linked to frontal lobe dysfunction. However, previous studies have relied exclusively on overt measures of memory and have not examined whether or not patients with false recognition continue to demonstrate preserved covert discrimination of familiar and unfamiliar items. Methods: We recorded skin conductance responses (SCRs) in a patient with frontal lobe damage and in normal control subjects while they performed a familiarity decision task using famous and unfamiliar faces as stimuli. Results: Patient J.S. produced significantly more overt false recognition errors and misidentifications in response to unfamiliar faces than control subjects. However, similar to the control subjects, he showed accurate covert autonomic discrimination of truly familiar faces from unfamiliar ones. Furthermore, SCRs to falsely recognized unfamiliar faces were not significantly different from SCRs generated to unfamiliar faces that J.S. correctly rejected. Conclusions: Our findings provide further neuropsychological evidence that overt and covert forms of face recognition memory are dissociable. In addition, the failure to detect an autonomic correlate for the false recognition errors and misidentifications in J.S. suggests that these memory distortions were not related to the spurious activation of stored memory representations for specific familiar faces. Instead, these incorrect responses may have been driven by the sense of familiarity evoked by novel faces that had a general resemblance to faces encountered previously. We propose that false recognition in J.S. resulted from the breakdown of strategic frontal memory retrieval, monitoring, and decision functions critical for attributing the experience of familiarity to its appropriate source.