Major depressive disorder and schizophrenia are associated with a disturbed experience of temporal memory

Background Disturbances in ‘psychological time’ are frequently reported in major depressive disorder (MDD) and schizophrenia. If one accepts the suggestion that the experience of the dimensions of time, past-present-future, are not inseparable then a disturbance in episodic memory is implicated. Episodic memory allows us to make sense of the world and our place within it by constructing a temporal context and temporal flow between events. These temporal representations are disordered in schizophrenia, but whether this is reflected in MDD is not known. Temporal-order memory deficits can be explained by two hypotheses. The prefrontal-organisational hypothesis suggests that deficits result from a breakdown in processes involved in encoding, retrieval, monitoring and decision-making. Whereas the hippocampal-mnemonic theory suggests that item-encoding, and inter-item associative encoding contribute to temporal-order memory. Methods New learning, recency judgments and executive function were investigated in 14 MDD patients, 15 schizophrenia patients and 10 healthy volunteers (HVs). Results Relative to HVs, both MDD and schizophrenia made more temporal errors despite achieving 100% learning. Deficits in executive function and item-recognition were present in both psychiatric groups, but executive function correlated to temporal errors in MDD only, and item-recognition to new learning in schizophrenia only. Limitations MDD and schizophrenia patients were taking medication Conclusions Temporal-ordering deficits are evident in both MDD and schizophrenia, and whilst the disruption of organisational and mnemonic processes appears to be ubiquitous, preliminary evidence from the correlational analysis suggests prefrontal problems are implicated in MDD temporal-order deficits, whereas hippocampal are more associated to temporal-order memory deficits in schizophrenia

Auditory recognition memory in schizophrenia using the remember/know paradigm

Aims: Auditory recognition memory was investigated in Schizophrenia in terms of remember (i.e. specific recollection) and know (i.e. familiarity without specific recollection) judgements. Methods: Three groups were investigated: normal controls (N=21) and patients diagnosed with Schizophrenia (N=10) and Major Depressive Disorder, Recurrent (N=10) according to DSM IV criteria. Participants were required to discriminate between previously heard sentences (targets) and novel sentences (distracters). Results: Results were analysed in terms of hit-rate frequency (number of correct targets), false-alarm rate frequency (number of false alarms), and signal-detection measures of A' (ability to discriminate between targets and distracters), and B''D (response bias i.e. probability of accepting a stimulus as a target when uncertain). Non-parametric tests showed no significant differences for hit-rate frequency, false-alarm rate frequency, A', and B''D. However, significant differences in remember (P<0.001) and know (P<0.05) were found. Patients with Schizophrenia made significantly more know judgements relative to normal controls (P<0.01) and significantly fewer remember judgements relative to normal controls (P<0.001) and patients with Major Depressive Disorder, Recurrent (P<0.01). Conclusions: Evidence suggests that amongst the reported cohort of patients with Schizophrenia; remember judgements play a significantly reduced contribution to auditory recognition memory compared to normal controls and patients with Major Depressive Disorder, Recurrent

Reality monitoring in anosognosia for hemiplegia

Anosognosia for hemiplegia (AHP) is a lack of awareness about paralysis following stroke. Recent explanations use a ‘forward model’ of movement to suggest that AHP patients fail to register discrepancies between internally- and externally-generated sensory information. We predicted that this failure would impair the ability to recall from memory whether information is internally- or externally-generated (i.e., reality monitor). Two experiments examined this prediction. Experiment 1 demonstrated that AHP patients exhibit a reality monitoring deficit for non-motor information (i.e., perceived vs. imagined drawings), whilst hemiplegic controls without anosognosia (nonAHP) perform like age-matched healthy volunteers (HVs). Experiment 2 explored if this deficit occurs when AHP patients discriminate performed, imagined, or observed movement. Results showed impaired reality monitoring for movements in AHP and nonAHP patients relative to HVs. Findings suggest that reality monitoring processes not directly related to movement, together with a failure to reality monitor movements, contribute to the pathogenesis of AHP

Visual object processing, reality monitoring, reasoning and visual hallucinations in Parkinson's disease

Up to 40% of patients with Parkinson’s disease will develop visual hallucinations at some point in their illness. Although medication, depression, duration of illness, and peripheral visual impairment have been identified as risk factors for hallucinations, more specific changes in cognitive function may also play a role. This pilot study evaluated 9 PD patients with visual hallucinations and 9 nonvisually-hallucinating PD patients on tests of imagery, recognition of objects, reasoning processes and reality monitoring. The reasoning processes tapped ability to derive a set of rules based on feedback, application of a strategy in relation to goal attainment and concept formation. Reality monitoring is defined as the normal process by which perceived and imagined events are discriminated in memory. In healthy volunteers, memories originating from experienced events have more contextual, perceptual and meaningful information than memories derived from internally generated events such as imagery processes, dreams and fantasies. However, if perceptual qualities of imagined events are unusually vivid, they may be more difficult to discriminate from perceived events. Our research revealed that visually hallucinating PD patients have greater difficulty with recognising visual objects viewed as either silhouettes (U=20.00, p=0.07) or when key identifying information which is hidden from view (U=22.00, p=0.05). Reasoning and reality monitoring processes were also deficient (both U=15.00, p=0.02). Errors in the reality monitoring task where most likely to occur for imagined items which were misattributed to perceived items. In contrast spatial processing, spatial imagery and visual object imagery showed higher levels of preservation. The findings from this study raise the possibility that visual hallucinations in PD could stem from a combination of impairments in visual object processing, particularly when key visual attributes of an item are obscured, reasoning and reality monitoring processes. Acknowledgements This work was supported by a Fasttrack grant from the Parkinson’s Disease Society

Recognition memory for neutral faces in depression

Aims: To determine whether major depressive disorder (MDD) gives rise to deficient recognition of neutral faces. Methods: 18 patients with MDD, according to DSM IV criteria, and 24 healthy volunteers were recruited. Patients were in remission during the study. Participants were required to discriminate 50 target faces (black and white photographs of male faces with neutral expressions), exposed for 3000 ms during a study phase, from 50 novel distracter faces introduced during the test phase. For all positive identifications (target hits as well as distracter false alarms) made during the test phase, participants indicated whether these were based on recollection of the face having been presented earlier, or limited to feelings of knowing/familiarity occurring in the absence of recollection. Results: The results were analysed in terms of overall recognition of faces using the signal detection measure d prime (d'), recollection rates (hit rate minus false alarm rate) and familiarity (d'). The MDD group was significantly impaired on measures of facial recognition memory (F = 15.05, p<0.001) and familiarity driven recognition decisions (F = 14.66, p<0.001). Recollection rates also approached significance (F = 3.93, p = 0.054). Conclusions: These findings suggest that MDD is not limited to only deficits in recognition of facial emotion cues, but also extends to recognition memory for neutral faces. Furthermore, this memory impairment is most evident in the processes which subserve feelings of familiarity. An abnormality in the subjective experience of familiarity may have clinical implications for patients’ reports of derealisation and depersonalisation. These findings also suggest that patients with MDD have impairments in familiarity driven recognition even when apparently recovered from an episode of illness