Martha Turner

Confabulation: damage to a specific inferior medial prefrontal system.

Confabulation, the pathological production of false memories, occurs following a variety of aetiologies involving the frontal lobes, and is frequently held to be underpinned by combined memory and executive deficits. However, the critical frontal regions and specific cognitive deficits involved are unclear. Studies in amnesic patients have associated confabulation with damage to the orbital and ventromedial prefrontal cortices. However, neuroimaging studies have associated memory-control processes which are assumed to underlie confabulation with the right lateral prefrontal cortex. We used a confabulation battery to investigate the occurrence and localisation of confabulation in an unselected series of 38 patients with focal frontal lesions. Twelve patients with posterior lesions and 50 healthy controls were included for comparison. Significantly higher levels of confabulation were found in the frontal group, confirming previous reports. More detailed grouping according to lesion location within the frontal lobe revealed that patients with orbital, medial and left lateral damage confabulated in response to questions probing personal episodic memory (PEM). Patients with orbital, medial and right lateral damage confabulated in response to questions probing orientation to time (OT). Performance-led analysis revealed that all patients who produced a total number of confabulations outside the normal range had a lesion affecting either the orbital region or inferior portion of the anterior cingulate. These data provide striking evidence that the critical deficit for confabulation has its anatomical location in the inferior medial frontal lobe. Performance on tests of memory and executive functioning showed considerable variability. Although a degree of memory impairment does seem necessary, performance on traditional executive tests is less helpful in explaining confabulation.

Distinct roles for lateral and medial rostral prefrontal cortex in source monitoring of perceived and imagined events

Rostral prefrontal cortex (PFC) is known to be involved in source memory, the ability to recollect contextual information about an event. However it is unclear whether subregions of rostral PFC may be differentially engaged during the recollection of different kinds of source detail. We used event related functional MRI to contrast two forms of source recollection: (1) recollection of whether stimuli had previously been perceived or imagined, and (2) recollection of which of two temporally distinct lists those stimuli had been presented in. Lateral regions of rostral PFC were activated in both tasks. However medial regions of rostral PFC were activated only when participants were required to recollect source information for self-generated, “imagined” stimuli, indicating a specific role in self-referential processing. In addition, reduced activity in a region of medial ventro-caudal PFC/basal forebrain was associated with making “imagined-to-perceived” confabulation errors. These results suggest that whilst the processing resources supported by some regions of lateral rostral PFC play a general role in source recollection, those supported by medial rostral PFC structures may be more specialised in their contributions.

Confabulation and delusion: a common monitoring framework.

Confabulations and delusions both involve the production of false claims. Although they may have different types of content, they share several characteristics. For example, they are often held with considerable conviction and are resistant to counter evidence, they may be acted upon, and they may be accompanied by a lack of concern about the false claim or its implications. Confabulations and delusions may initially arise from failures in different systems (e.g., mnemonic vs. perceptual or affective). However, their shared characteristics raise the possibility that the monitoring deficits involved might be the same, resulting in failure to reject the confabulatory or delusional ideas. In this paper we will focus on the nature of these common monitoring deficits. Critically, we argue that monitoring in confabulation and delusion involves both unconscious and conscious processes. We propose that an unconscious process is responsible for tagging suspect content which needs to be checked for veracity by a separate set of conscious evaluative processes. Failure of these monitoring processes would allow ideas which ought to be checked and rejected to instead be uncritically accepted: This would result in the production of confabulations or delusions. Importantly, inclusion of both unconscious and conscious monitoring stages allows the model to account for both “endorsement” and “explanation” delusions, and both “primary” and “secondary” confabulations. Our hope is that this model may provide a theoretical framework to guide empirical investigation of the commonalities and differences between the conditions.

Advantages of the multiple case series approach to the study of cognitive deficits in autism spectrum disorder

In the neuropsychological case series approach, tasks are administered that tap different cognitive domains, and differences within rather than across individuals are the basis for theorising; each individual is effectively their own control. This approach is a mainstay of cognitive neuropsychology, and is particularly suited to the study of populations with heterogeneous deficits. However it has very rarely been applied to the study of cognitive differences in autism spectrum disorder (ASD). Here, we investigate whether this approach can yield information beyond that given by the typical group study method, when applied to an ASD population. Twenty-one high-functioning adult ASD participants and 22 IQ, age, and gender-matched control participants were administered a large battery of neuropsychological tests that would represent a typical neuropsychological assessment for neurological patients in the United Kingdom. The data were analysed using both group and single-case study methods. The group analysis revealed a limited number of deficits, principally on tests with a large executive function component, with no impairment in more routine abilities such as basic attending, language and perception. Single-case study analysis proved more fruitful revealing evidence of considerable variation in abilities both between and within ASD participants. Both sub-normal and supra-normal performance were observed, with the most defining feature of the ASD group being this variability. We conclude that the use of group-level analysis alone in the study of cognitive deficits in ASD risks missing cognitive characteristics that may be vitally important both theoretically and clinically, and even may be misleading because of averaging artifact.

Normal social cognition in developmental prosopagnosia

Face perception provides information critical to cognitive computations about the social world. This raises the possibility that the development of mechanisms used for social cognition may depend on the presence of normal face perception mechanisms, and this notion partly motivates an aetiological model of autism spectrum disorder (ASD) that suggests that deficits in face perception lead to the social cognition impairments that characterize ASD. To investigate these issues, we examined social cognition in participants with developmental prosopagnosia (DP). A total of 2 male DPs with severe facial identity and facial expression deficits showed no signs of impaired social cognition on three measures. A total of 10 other DPs responded to an inventory measuring autistic traits, and all except one performed normally. These results indicate that social cognition mechanisms can develop normally in the context of developmental face-processing impairments.

Developing hypnotic analogues of clinical delusions: Mirrored-self misidentification

Introduction. Despite current research interest in delusional beliefs, there are no viable models for studying delusions in the laboratory. However, hypnosis offers a technique for creating transient delusions that are resistant to challenge. The aim of this study was to develop an hypnotic analogue of one important delusion, mirrored-self misidentification. Methods. Twelve high hypnotisable participants received an hypnotic suggestion to see either a stranger in the mirror, a mirror as a window, or a mirror as a window with a view to a stranger. Participants’ deluded beliefs were challenged, and following hypnosis, Sheehan and McConkeys (1982) Experiential Analysis Technique was used to explore participants’ phenomenological experience of the delusion. Results. The majority of participants did not recognise their reflection in the mirror, described the person in the mirror as having different physical characteristics to themselves, and maintained their delusion when challenged. Conclusions. The hypnotic suggestion created a credible, compelling delusion with features strikingly similar to clinical cases of mirrored-self misidentification. Our findings suggest that Factor 2 within Langdon and Colthearts (2000) two-factor framework may involve a lowering of the criteria used to accept or reject delusional hypotheses.

Impairments in proverb interpretation following focal frontal lobe lesions

The proverb interpretation task (PIT) is often used in clinical settings to evaluate frontal “executive” dysfunction. However, only a relatively small number of studies have investigated the relationship between frontal lobe lesions and performance on the PIT. We compared 52 patients with unselected focal frontal lobe lesions with 52 closely matched healthy controls on a proverb interpretation task. Participants also completed a battery of neuropsychological tests, including a fluid intelligence task (Raven’s Advanced Progressive Matrices). Lesions were firstly analysed according to a standard left/right sub-division. Secondly, a finer-grained analysis compared the performance of patients with medial, left lateral and right lateral lesions with healthy controls. Thirdly, a contrast of specific frontal subgroups compared the performance of patients with medial lesions with patients with lateral frontal lesions. The results showed that patients with left frontal lesions were significantly impaired on the PIT, while in patients with right frontal lesions the impairments approached significance. Medial frontal patients were the only frontal subgroup impaired on the PIT, relative to healthy controls and lateral frontal patients. Interestingly, an error analysis indicated that a significantly higher number of concrete responses were found in the left lateral subgroup compared to healthy controls. We found no correlation between scores on the PIT and on the fluid intelligence task. Overall our results suggest that specific regions of the frontal lobes contribute to the performance on the PIT.

Delusion and confabulation: Overlapping or distinct distortions of reality?

Delusion is commonly defined as a false belief and associated with psychiatric illness like schizophrenia, whereas confabulation is typically described as a false memory and associated with neurological disorder like amnesia. Yet delusion and confabulation both involve the endorsement of distorted representations of reality, whether about the present or the personal past. Moreover, differences in aetiology need not dictate mutual exclusivity with regard to underlying cognitive mechanisms. In response to the growing interest in commonalities and differences between delusion and confabulation, this Special Issue brings together contributors from diverse fields to consider the relations between these two symptoms. Although approaches and opinions differ, all of our contributors share common aims of clarifying theoretical conceptions and exploring boundaries so as to advance understanding of the cognitive neuropsychiatry of both delusion and confabulation. After introducing each contribution, we highlight some common themes and unanswered questions.

Spontaneous confabulation, temporal context confusion and reality monitoring: a study of three patients with anterior communicating artery aneurysms.

Spontaneous confabulation involves the production of false or distorted memories, and is commonly associated with ventromedial prefrontal damage. One influential theory proposes that the critical deficit is a failure to suppress currently irrelevant memory traces that intrude into ongoing thinking (Schnider & Ptak, 1999). In this study, we report experimental investigations with three spontaneously confabulating patients aimed at exploring this account. Using Schnider and Ptaks (1999) continuous recognition paradigm, we replicated their experimental results with our patients. However, our data suggest that the critical impairment might be more generalized than a failure to suppress currently irrelevant memories. First, a temporal source monitoring task failed to show that previous memory traces intrude into the present. Second, a reality monitoring task revealed that confabulating patients had a tendency to misidentify imagined events as real, a result that cannot be explained in terms of temporal confusion. This error was specific to confabulating patients and was not shared by non-confabulating ACoA patients. Our data therefore suggest a more generalized impairment in source monitoring, not only on the basis of temporality or current relevance, but across a range of contextual domains, including information used to distinguish real memories from imaginings.

The effect of age on cognitive performance of frontal patients

Age is known to affect prefrontal brain structure and executive functioning in healthy older adults, patients with neurodegenerative conditions and TBI. Yet, no studies appear to have systematically investigated the effect of age on cognitive performance in patients with focal lesions. We investigated the effect of age on the cognitive performance of a large sample of tumour and stroke patients with focal unilateral, frontal (n=68), or non-frontal lesions (n=45) and healthy controls (n=52). We retrospectively reviewed their cross sectional cognitive and imaging data. In our frontal patients, age significantly predicted the magnitude of their impairment on two executive tests (Ravens Advanced Progressive Matrices, RAPM and the Stroop test) but not on nominal (Graded Naming Test, GNT) or perceptual (Incomplete Letters) task. In our non-frontal patients, age did not predict the magnitude of their impairment on the RAPM and GNT. Furthermore, the exacerbated executive impairment observed in our frontal patients manifested itself from middle age. We found that only age consistently predicted the exacerbated executive impairment. Lesions to specific frontal areas, or an increase in global brain atrophy or white matter abnormalities were not associated with this impairment. Our results are in line with the notion that the frontal cortex plays a critical role in aging to counteract cognitive and neuronal decline. We suggest that the combined effect of aging and frontal lesions impairs the frontal cortical systems by causing its computational power to fall below the threshold needed to complete executive tasks successfully.