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.

Fear recognition deficits after focal brain damage: a cautionary note.

OBJECTIVE: To test the hypothesis that fear recognition deficits in neurologic patients reflect damage to an emotion-specific neural network. BACKGROUND: Previous studies have suggested that the perception of fear in facial expressions is mediated by a specialized neural system that includes the amygdala and certain posterior right-hemisphere cortical regions. However, the neuropsychological findings in patients with amygdala damage are inconclusive, and the contribution of distinct cortical regions to fear perception has only been examined in one study. METHODS: We studied the recognition of six basic facial expressions by asking subjects to match these emotions with the appropriate verbal labels. RESULTS: Both normal control subjects (n = 80) and patients with focal brain damage (n = 63) performed significantly worse in recognizing fear than in recognizing any other facial emotion, with errors consisting primarily of mistaking fear for surprise. Although patients were impaired relative to control subjects in recognizing fear, we could not obtain convincing evidence that left, right, or bilateral lesions were associated with disproportionate impairments of fear perception once we adjusted for differences in overall recognition performance for the other five facial emotion categories. The proposed special role of the amygdala and posterior right-hemisphere cortical regions in fear perception was also not supported. CONCLUSIONS: Fear recognition deficits in neurologic patients may be attributable to task difficulty factors rather than damage to putative neural systems dedicated to fear perception.

Word-stem completion priming for perceptually and conceptually encoded words in patients with Alzheimer's disease.

This study examined whether the frequently reported word-stem completion priming deficit of Alzheimer's disease (AD) patients could be characterized as either a semantic encoding deficit or a conceptual priming deficit. AD patients and normal elderly control subjects studied words in two conditions: (1) reading visually presented words aloud, which maximizes perceptual encoding of seen words, and (2) generating words aloud from definitions, which maximizes conceptual encoding of words not seen but retrieved on the basis of semantic context. Recognition accuracy was greater for words that were generated at study, and word-stem completion priming was greater for words that were read at study. For the AD patients, recognition accuracy was impaired and word-stem completion priming was intact for words encoded in both conditions. The findings are discussed in terms of discrepant results about word-stem completion priming in AD.

Preserved priming across study-test picture transformations in patients with Alzheimer's disease.

Picture-naming priming was examined across different study-test transformations to explore the nature of memory representations of objects supporting implicit memory processes in patients with Alzheimer's disease (AD). Although severely impaired in explicit memory for pictures and words, AD patients demonstrated normal priming across perceptual transformations in picture orientation (Experiment 1) and picture size (Experiment 2) and across symbolic transformations from words to pictures (Experiment 3). In addition, the priming across alterations in picture size was invariant. This demonstrates that AD patients have preserved implicit memory for high-level, abstract representations of objects.

Intact text-specific implicit memory in patients with Alzheimer's disease.

The ability of patients with Alzheimer's disease (AD) to acquire and retain text-specific knowledge was investigated in a re-reading study. Patients and normal control Ss read 2 passages 3 times, each as quickly as possible, and answered recognition memory questions after the 3rd reading of each passage. The AD patients had poor explicit memory as evidenced by impaired recognition memory for the passages. In contrast, normal decreases in the times required for successive readings of each passage for AD patients indicated intact implicit memory for the passages. The absence of facilitation across passages indicated that the re-reading effect was text specific, suggesting that AD patients may retain the ability to form certain kinds of implicit new associations. Alternative accounts of the mechanism underlying text-specific priming, and of the nature of intact and impaired implicit memory in AD, are considered.

Sources of priming in text rereading: intact implicit memory for new associations in older adults and in patients with Alzheimer's disease.

The contributions of text meaning, new between-word associations, and single-word repetition to priming in text rereading in younger and older adults, and in patients with Alzheimer's disease. (AD), were assessed in Experiment 1. Explicit recognition memory for text was also assessed. Equivalent single-word and between-word priming was observed for all groups, even though patients with AD showed impaired explicit memory for individual words in the text. The contribution of generalized reading task skill to priming in meaningless text rereading in younger adults was assessed in Experiment 2. Generalized reading task skill was also found to contribute to priming. These results reveal 3 mechanisms of priming: new between-word associations for meaningful and meaningless text, individual word repetition for meaningless text, and general task or skill factors for meaningless text. All priming mechanisms appear to be intact in older adults and in patients with AD.

Reduced frontal white matter volume in long-term childhood leukemia survivors: a voxel-based morphometry study.

BACKGROUND AND PURPOSE: To our knowledge, no published studies have examined whole-brain regional differences to identify more discrete volumetric changes in the brains of childhood leukemia survivors. We used voxel-based morphometry (VBM) to examine regional gray and white matter differences in a group of long-term survivors of acute lymphoblastic leukemia (ALL) compared with a group of healthy controls. Differences in regional white matter volume were expected, given previous reports of white matter changes during treatment for ALL and reduced brain white matter volumes in long-term survivors. Follow-up analyses examined the relationship of regional brain volumes to cognitive function. MATERIALS AND METHODS: We compared 9 long-term survivors of ALL with 14 healthy controls. Survivors of ALL were treated with systemic and intrathecal chemotherapy only. T1-weighted axial 3D spoiled gradient high-resolution images collected on a 1.5T MR imaging scanner were used for the VBM analysis. Neuropsychological evaluations were conducted within 2 months of the MR imaging to assess cognitive function. RESULTS: VBM analysis revealed 2 specific regions of reduced white matter in the right frontal lobes of survivors of ALL compared with healthy controls. Survivors of ALL had lower performances on tests of attention, visual-constructional skills, mental flexibility, and math achievement compared with healthy individuals. Decreased performance on neuropsychological measures was associated with decreased regional white matter volumes. No differences were found between the groups with respect to gray matter regions. CONCLUSION: These findings are consistent with previous literature describing the long-term cognitive, academic, and imaging findings of survivors of ALL and suggest that right frontal white matter is particularly vulnerable to disruption following intensive chemotherapy for ALL. Future studies should focus on further clarifying the white matter changes observed.

Object decision priming in Alzheimer's disease.

Priming for line drawings of real and nonreal objects was examined in an object decision task for 16 patients with Alzheimer's disease (AD) and 16 normal elderly control (NC) participants. In two study phases, participants decided if objects were real or nonreal. In an implicit test phase, real/nonreal decisions were made for studied and unstudied objects, and priming was measured as the difference in decision speed or accuracy between studied and unstudied objects. In an explicit test phase, yes/no recognition was measured for real and nonreal objects. AD patients had impaired explicit memory for real and nonreal objects and intact repetition priming for real objects. By the latency measure, both AD and NC groups showed priming for nonreal objects but in opposite ways. Classification decisions about studied relative to nonstudied nonreal objects were slower for the AD patients, whereas such decisions were faster for the NC participants. Classification decisions of both groups were less accurate for repeated nonreal objects. These results support the claim that AD patients with mild cognitive impairment show normal perceptual priming. The AD inhibition for studied nonreal objects is discussed in terms of the decision conflict that occurs when recollection of source is not available to counter the influence of familiarity.