Testing the connections within face processing circuitry in Capgras delusion with diffusion imaging tractography

Pupil dilation reflects covert familiar face recognition under interocular suppression

In prosopagnosia, brain lesions impair overt face recognition, but not face detection, and may coexist with residual covert recognition of familiar faces. Previous studies that simulated covert recognition in healthy individuals have impaired face detection as well as recognition, thus not fully mirroring the deficits in prosopagnosia. We evaluated a model of covert recognition based on continuous flash suppression (CFS). Familiar and unfamiliar faces and houses were masked while participants performed two discrimination tasks. With increased suppression, face/house discrimination remained largely intact, but face familiarity discrimination deteriorated. Covert recognition was present across all masking levels, evinced by higher pupil dilation to familiar than unfamiliar faces. Pupil dilation was uncorrelated with overt performance across subjects. Thus, CFS can impede overt face recognition without disrupting covert recognition and face detection, mirroring critical features of prosopagnosia. CFS could be used to uncover shared neural mechanisms of covert recognition in prosopagnosic patients and neurotypicals.

What is Capgras delusion?

INTRODUCTION

Capgras delusion is sometimes defined as believing that close relatives have been replaced by strangers. But such replacement beliefs also occur in response to encountering an acquaintance, or the voice of a familiar person, or a pet, or some personal possession. All five scenarios involve believing something familiar has been replaced by something unfamiliar.

METHODS

We evaluate the proposal that these five kinds of delusional belief should count as subtypes of the same delusion.

RESULTS

Personally familiar stimuli activate the sympathetic nervous system (SNS) much more strongly than unfamiliar stimuli. In Capgras delusion, this difference is absent, prompting the delusional idea that a familiar person is actually a stranger. We suggest this absence of an effect of familiarity on SNS response will occur in all five scenarios and will prompt the idea that the familiar has been replaced by the unfamiliar.

CONCLUSIONS

We propose that: (a) all five scenarios be referred to as subtypes of Capgras delusion; (b) in all five, ideas about replacement are prompted by weakness of SNS responses to familiar stimuli; (c) this is insufficient to generate delusion. For a delusional idea to become a belief, a second factor (impaired hypothesis evaluation) must also be present.

Failure of hypothesis evaluation as a factor in delusional belief

INTRODUCTION

In accounts of the two-factor theory of delusional belief, the second factor in this theory has been referred to only in the most general terms, as a failure in the processes of hypothesis evaluation, with no attempt to characterise those processes in any detail. Coltheart and Davies ([2021]. How unexpected observations lead to new beliefs: A Peircean pathway. Consciousness and Cognition, 87, 103037. https://doi.org/10.1016/j.concog.2020.103037) attempted such a characterisation, proposing a detailed eight-step model of how unexpected observations lead to new beliefs based on the concept of abductive inference as introduced by Charles Sanders Peirce.

METHODS

In this paper, we apply that model to the explanation of various forms of delusional belief.

RESULTS

We provide evidence that in cases of delusion there is a specific failure of the seventh step in our model: the step at which predictions from (delusional) hypotheses are considered in the light of relevant evidence.

CONCLUSIONS

In the two-factor theory of delusional belief, the second factor consists of a failure to reject hypotheses in the face of disconfirmatory evidence.

Anatomical connections underlying personally-familiar face processing

Familiar face processing involves face specific regions (the core face system) as well as other non-specific areas related to processing of person-related information (the extended face system). The connections between core and extended face system areas must be critical for face recognition. Some studies have explored the connectivity pattern of unfamiliar face responding area, but none have explored those areas related to face familiarity processing in the extended system. To study these connections, diffusion weighted imaging with probabilistic tractography was used to estimate the white-matter pathways between core and extended system regions, which were defined from functional magnetic resonance imaging responses to personally-familiar faces. Strong white matter connections were found between occipitotemporal face areas (OFA/FFA) with superior temporal sulcus and insula suggesting the possible existence of direct anatomical connections from face-specific areas to frontal nodes that could underlay the processing of emotional information associated to familiar faces.

Positive emotional reactions to loved names

Studies concerning personal attachment have successfully used loved familiar faces to prompt positive affective and physiological reactions. Moreover, the processing of emotional words shows similar physiological patterns to those found with affective pictures. The objective of this study was to assess whether the passive viewing of loved names would produce a pattern of subjective and physiological reactivity similar to that produced by the passive viewing of loved faces. The results showed that, compared to neutral (unknown) and famous names, loved names produced a biphasic pattern of heart rate deceleration-acceleration, heightened skin conductance and zygomaticus muscle activity, inhibition of corrugator muscle activity, and potentiation of the startle reflex response. This pattern of physiological responses was accompanied by subjective reports of higher positive affect and arousal for loved names than for neutral and famous ones. These findings highlight not only the similarity but also the differences between the affective processing of identity recognition by loved faces and names.

Capgras' Delusion: A Systematic Review of 255 Published Cases

BACKGROUND

Capgras' delusion has captured psychiatrists' imaginations, but the clinical features of the delusion have rarely been studied and presented systematically.

AIMS

The present study systematically reviews all case reports on Capgras' delusion in the English language in order to better understand differences between organic and functional aetiologies.

METHODS

All medical and psychiatric databases were searched, as were the bibliographies of published case reports, narrative reviews, and book chapters.

RESULTS

A total of 258 cases were identified from 175 papers. Functional Capgras' delusion was more associated with a wider variety of imposters; multiple imposters; other misidentification syndromes; auditory hallucinations; other delusions; and formal thought disorder. Organic cases were associated with age; inanimate objects; memory and visual-spatial impairments; right hemispheric dysfunction; and visual hallucinations. Executive dysfunction and aggression were associated with both types.

CONCLUSIONS

Specific features of the -Capgras' delusional content and associated signs point to either organic or functional aetiology. The delusion is more amorphous than many theorists have supposed, which challenges their explanatory models.

Transient Capgras Syndrome Secondary to Bilateral Ischemic Stroke: A Case Report

Capgras syndrome is one of a variety of delusional misidentification syndromes that can be associated with acute ischemic stroke, neurodegenerative disease, or metabolic conditions. Most cases reported in the literature are associated with frontal and/or parietal lobe involvement. Transient Capgras syndrome is rare but has been reported. We present a case of transient Capgras syndrome following bilateral cerebral ischemic infarcts in the frontal, parietal, and temporal regions, and involving the right prefrontal cortex. To our knowledge, transient Capgras syndrome with rapid resolution over a period of days is rare.

"Capgras" Delusions Involving Belongings, Not People, and Evolving Visual Hallucinations Associated with Occipital Lobe Seizures

Capgras syndrome is characterized by the delusional belief that a familiar person has been replaced by a visually similar imposter or replica. Rarely, the delusional focus may be objects rather than people. Numerous etiologies have been described for Capgras to include seizures. Similarly, visual hallucinations, both simple and complex, can occur secondary to seizure activity. We present, to our knowledge, the first reported case of visual hallucinations and Capgras delusions for objects that developed secondary to new onset occipital lobe epilepsy. We then discuss the possible underlying neurologic mechanisms responsible for the symptomatology.