Nicola M.J. Edelstyn

Bilateral dorsolateral thalamic lesions disrupts conscious recollection

In an earlier study we disputed the claim that the mediodorsal thalamic nucleus is critical for familiarity. We reported patient (QX) who showed a severe deficit in conscious recollection, and behavioural problems (disinhibition, emotional lability) with relative sparing of familiarity-aware memory following a left mediodorsal thalamic lesion. More recent MR imaging has revealed that QXs lesions are more extensive than previously reported and involve both dorsolateral thalamic nuclei, and whilst there is evidence of left mediodorsal thalamic damage, it is not the main focus of damage. This paper reports a full analysis of QXs thalamic pathology alongside a more detailed investigation of his recognition memory, using yes/no and forced-choice procedures, and executive function. The results revealed impairments in yes/no recognition and conscious recollection rates of famous, artist and unknown names. In addition to the previously noted behavioural disinhibition and emotional lability, a deficit in spontaneous planning ability was evident on the Zoo Map Test (subtest of the Bahavioural Assessment of the Dysexecutive Syndrome). Forced-choice recognition, familiarity estimates and remote memory showed higher levels of preservation. The findings indicate that the dorsolateral thalamus is part of the extended hippocampal circuit which is causally critical only for recall and conscious recollection of complex associations rather than for the more automatic processes linked with novelty detection.

Contribution of the left dorsomedial thalamus to recognition memory: a neuropsychological case study.

This study reports a patient with a unilateral left thalamic lesion which was centred on the dorsomedial thalamic nucleus. Cognitive neuropsychological assessment revealed a severe impairment in verbal memory and symptoms of executive dysfunction, in the presence of relatively intact visual and facial recognition, working memory, praxis, language and IQ. Verbal and visual recognition memory were investigated using the remember-know paradigm. The results indicated a profound impairment in recollection-driven verbal recognition memory. These results are discussed in the context of the role of the dorsomedial thalamic nucleus in recognition memory, and functional models of memory.

The Delusions of Capgras and Intermetamorphosis in a Patient with Right-Hemisphere White-Matter Pathology

Previous neuropsychological studies have demonstrated an association between person misidentification and right-hemisphere dysfunction. In the study reported here, we explore the contribution of facial and visual recognition impairments in a patient with right-hemisphere subcortical white-matter pathology in the frontal and parietal lobes and a diagnosis of vascular cognitive impairment. The patient displayed false recognition of unfamiliar faces and deficient retrieval of key biographic detail for famous faces. These results are discussed in the context of the contribution of deficiencies in the visual system and subcortical white-matter lesions to the development of Capgras delusion.

Why are some Parkinson disease patients unaware of their dyskinesias

ObjectiveTo test the hypothesis that anosognosia for dyskinesias in Parkinson disease (PD) results from a failure to detect discrepancies between intended and actual movement. BackgroundPD patients often complain of drug-induced dyskinesias (involuntary movements) less than their carers. This remarkable unawareness is an example of anosognosia (ie, unawareness of deficits associated with an illness). A better understanding of anosognosia for dyskinesias in PD is important to understand the impact of the illness and side effects of treatment. MethodsThe ability to detect a discrepancy between intended movement and visual feedback about actual movement was investigated in 6 PD patients with anosognosia for dyskinesias, 11 nonanosognosic PD controls with dyskinesias, and 22 healthy volunteers, using a mirror to reverse the expected visual consequences of an executed movement. ResultsNonanosognosic PD patients and healthy volunteers rated mirror-reversed movement as significantly stranger than normal movement (P=0.024 and <0.001, respectively), whereas PD patients with anosognosia for dyskinesias did not (P=0.375). ConclusionsThe findings support our proposal, in that PD patients with anosognosia for dyskinesias do not report mirror-reversed movement (in which intentions and visual feedback conflict) as feeling distinct from normal movement.

Effect of click trains on duration estimates by people with Parkinson's disease.

Patients with a diagnosis of Parkinsons disease and age- and IQ-matched controls estimated the duration of short 500-Hz tones (325–1,225 ms), on trials where the tone was either preceded by 3 s of 5-Hz clicks, or presented without clicks. The click manipulation had been shown in earlier studies with student participants to make verbal estimates longer. Patients were tested both on and off their dopaminergic medication, and controls were also tested in two sessions. Verbal estimates were markedly and significantly longer on trials with clicks than on those without clicks for both the patients and the controls, but there were no significant performance differences between patients or controls, nor between the on and off medication sessions in the patients. The study shows that a manipulation of subjective time, which has had small but consistent effects in student participants, also affects timing in patients and adds to a growing body of evidence that timing in patients with Parkinsons disease may in many cases have the same characteristics as those of neurologically intact control groups.

Impairment in material-specific long-term memory following unilateral mediodorsal thalamic damage and presumed partial disconnection of the mammillo-thalamic tract

Neuropsychological findings suggest material-specific lateralization of the medial temporal lobes role in long-term memory, with greater left-sided involvement in verbal memory, and greater right-sided involvement in visual memory. Whether material-specific lateralization of long-term memory also extends to the anteromedial thalamus remains uncertain. We report two patients with unilateral right (OG) and left (SM) mediodorsal thalamic pathology plus probable correspondingly lateralized damage of the mammillo-thalamic tract. The lesions were mapped using high-resolution structural magnetic resonance imaging and schematically reconstructed. Mean absolute volume estimates for the mammillary bodies, hippocampus, perirhinal cortex, and ventricles are also presented. Estimates of visual and verbal recall and item recognition memory were obtained using the Doors and People, the Rey Complex Figure Test, and the Logical Memory subtests of the Wechsler Memory Scales. Each patients performance was compared to a group of healthy volunteers matched for demographic characteristics, premorbid IQ, and current levels of functioning. A striking double dissociation was evident in material-specific long-term memory, with OG showing significant impairments in visual memory but not verbal memory, and SM showing the opposite profile of preserved visual memory and significantly impaired verbal memory. These impairments affected both recall and item recognition. The reported double dissociation provides the strongest evidence yet that material-specific lateralization of long-term memory also extends to the anteromedial thalamus. The findings are also discussed in relation to proposals that distinct anatomical regions within the medial temporal lobe, anteromedial thalamus, and associated tracts make qualitatively different contributions to recall and item recognition.

Recollection deficiencies in patients with major depressive disorder.

Neuropsychological research suggests that recognition memory (RM) and recall memory are impaired in patients with a major depressive disorder or a dysphoric mood state. This study examines the proposal that abnormalities in recollection (a form of recall) result from a breakdown in frontal strategic memory processes involved in encoding and retrieval, and executive functions linked to reality monitoring, planning, problem-solving, reasoning and decision-making. We investigated two predictions arising from this theory. Firstly, patients diagnosed with a major depressive disorder (MDD) will display a dissociation between (deficient) recollection and (preserved) familiarity. Secondly, if recollection impairments are indicative of a breakdown in prefrontal strategic memory processes which are dependent, at least in part, on executive processes, then an explicit correlational approach predicts that recollection will be positively associated with the severity of executive dysfunction in MDD patients. The remember/know paradigm was used to investigate RM for words and neutral faces in 16 MDD patients and 16 healthy volunteers, matched for age, gender and estimates of premorbid IQ. Measures of executive function included working memory, reasoning and decision-making. Applying the Dual Process Signal Detection interpretation of the remember/know data, the MDD group displayed significant impairments in RM and recollection rates for both verbal and neutral facial memoranda. In contrast, familiarity-aware rates were preserved. There was no evidence of executive dysfunction in the patient group, and little evidence that recollection rates correlated with executive function. Furthermore, a single process signal detection approach suggested that the MDD patients displayed a reduction in sensitivity for RM and remember rates but not know responses. The criteria for detecting studied from unstudied items, and remembering from knowing, were the same in both patient and healthy control groups. Taken together, these findings are consistent with the view that MDD is marked by a decline in RM, which is underpinned by an impairment in recollection rather than familiarity processes. The extent to which the recollection deficiencies arise from disruption of strategic memory and executive processes requires further investigation.

Auditory Recognition Memory, Conscious Recollection, and Executive Function in Patients with Schizophrenia

Background: Dual-process models propose that recognition memory (RM) involves two processes: conscious recollection and familiarity-aware memory. Studies investigating RM in schizophrenia report a selective deficit in conscious recollection and intact levels of familiarity-driven RM for stimuli presented in the visual and olfactory domains. It has been suggested that abnormalities in conscious recollection result from a breakdown in frontal strategic memory processes involved in encoding and retrieval and executive functions linked to reality monitoring and decision making. We investigated three predictions arising from these proposals. Firstly, if conscious recollection abnormalities arise from a central impairment, then these abnormalities should not be domain specific. Secondly, if the deficits in conscious recollection arise from a breakdown in executive processes, deficiencies should be correlated with executive dysfunction. Finally, the conscious recollection deficiencies are likely to be more severe in schizophrenia, a condition associated with marked executive dysfunction relative to Major Depressive Disorder, Recurrent (MDDR), in which executive dysfunction is less marked. Methods: The remember/know paradigm was used to investigate RM for voices in three groups: patients with schizophrenia (n = 14), patients with MDDR (n = 16), and normal controls (n = 16). Executive function was assessed using the Wisconsin Card Sorting Task. Results: Patients with schizophrenia made significantly fewer remember responses than normal controls (p < 0.01), despite normal levels of discrimination and familiarity-driven auditory RM. Patients with MDDR did not differ significantly from either normal controls or patients with schizophrenia. Executive dysfunction was limited to the schizophrenia group and was not correlated with conscious recollection deficiencies. Conclusions: Patients with schizophrenia exhibit a deficit in conscious recollection for auditory RM of voices. These findings, when considered alongside remember/know data collected from the same set of patients for olfactory and visual RM, support proposals that abnormalities in conscious recollection stem from a breakdown in central rather than domain-specific processes.

Investigation of Conscious Recollection, False Recognition and Delusional Misidentification in Patients with Schizophrenia

Background: Recognition memory (RM) is impaired in patients with schizophrenia, as they rely largely on feelings of familiarity rather than conscious recollection. It has been suggested that this abnormality may reflect a breakdown in strategic memory processes involved in both encoding and retrieval. By studying 2 patients with false recognition (FR; patient C.T.) and delusional misidentification (DM; patient B.C.), and a group of psychotic control patients, we examined proposals that FR and DM exist on a continuum of increasingly severe impairment in strategic memory function. Methods: Executive function, autobiographical memory and verbal and facial RM were assessed using standard neuropsychological tests and the remember/know paradigm. Results: The psychotic control group displayed a significantly reduced reliance on remember judgements and compensatory elevation in know judgements on both RM tasks compared with the normal control group. Patient B.C. also followed this trend, but in a much more pronounced manner. In contrast, patient C.T. displayed a qualitatively different performance profile, which was marked by an increased dependence on remember responses. Conclusions: We have presented evidence which support proposals that a breakdown in strategic memory and executive dysfunction are more pronounced in DM than FR. However, the small sample size precludes any firm conclusions being drawn.

Does autonomic arousal distinguish good and bad decisions? Healthy individuals’ skin conductance reactivity during the Iowa Gambling Task

The somatic marker hypothesis (SMH) proposes that physiological feedback to the brain influences cognitive appraisal and human decisions, however, the strength of evidence in support of the SMH is equivocal. We examined the validity of the SMH by measuring physiological arousal in a population of healthy individuals playing the Iowa Gambling Task (IGT), which is a computerized card game designed to assess real-life decisions. We also examined the influence of reinforcer type on IGT performance and physiological reactivity. Skin conductance level (SCL) reactivity was measured in 41 participants performing the IGT using either facsimile or real money. Participants were categorized as normal (i.e., nonimpaired) or impaired on the basis of their IGT performance, and differences in performance and physiological reactivity between groups were examined. No differences in SCL were found between normal and impaired groups. However, greater SCL rises were borderline significant when anticipating choices from bad de...