Sebastian Dieguez

Is poststroke depression a vascular depression

As we learn more about the relationships between depression and cerebrovascular disease (CVD), a complex picture is emerging in which the chain of causality seems to spiral on itself: progressive or focal brain damage, cognitive impairment, depressive symptoms, dementia, and cardiovascular diseases, all seem to be liable to lead to one or another. Stroke may lead to depression, and the inverse may also be true. Depression may lead to cognitive impairment and cardiovascular diseases, which in turn may lead to subtle brain impairment, thereby causing more depression and cognitive impairments, and so on. In this presentation, we provide a rapid glance at the complexities of such issues.

Illusory own body perceptions: case reports and relevance for bodily self-consciousness

Neurological disorders of body representation have for a long time suggested the importance of multisensory processing of bodily signals for self-consciousness. One such group of disorders--illusory own body perceptions affecting the entire body--has been proposed to be especially relevant in this respect, based on neurological data as well as philosophical considerations. This has recently been tested experimentally in healthy subjects showing that integration of multisensory bodily signals from the entire body with respect to the three aspects: self-location, first-person perspective, and self-identification [corrected], is crucial for bodily self-consciousness. Here we present clinical and neuroanatomical data of two neurological patients with paroxysmal disorders of full body representation in whom only one of these aspects, self-identification, was abnormal. We distinguish such disorders of global body representation from related but distinct disorders and discuss their relevance for the neurobiology of bodily self-consciousness.

Seeing the phantom: A functional magnetic resonance imaging study of a supernumerary phantom limb†

Supernumerary phantom limb (SPL) is a rare neurological manifestation where patients with a severe stroke‐induced sensorimotor deficit experience the illusory presence of an extra limb that duplicates a real one. The illusion is most often experienced as a somesthetic phantom, but rarer SPLs may be intentionally triggered or seen. Here, we report the case of a left visual, tactile, and intentional SPL caused by right subcortical damage in a nondeluded woman.

Leaving Body and Life Behind: Out-of-Body and Near-Death Experience

Out-of-body experiences (OBEs) and near-death experiences (NDEs) are complex phenomena that have fascinated mankind from time immemorial. OBEs are defined as experiences in which a person seems to be awake and sees his body and the world from a disembodied location outside his physical body. Recent neurological and neuroscientific research suggests that OBEs are the result of disturbed bodily multisensory integration, primarily in right temporo-parietal cortex. NDEs are more loosely defined, and refer to a set of subjective phenomena, often including an OBE, that are triggered by a life-threatening situation. Although a number of different theories have been proposed about the putative brain processes underlying NDEs, neurologists and cognitive neuroscientists have, so far, paid little attention to these phenomena, although several experimental investigations based on principles from cognitive neuroscience are possible. This might be understandable but is unfortunate, because the neuroscientific study of NDEs could provide insights into the functional and neural mechanisms of beliefs, concepts, personality, spirituality, magical thinking, and the self. Based on previous medical and psychological research in cardiac arrest patients with NDEs, we sketch a neurological framework for the study of the so-called NDEs.

Nothing Happens by Accident, or Does It? A Low Prior for Randomness Does Not Explain Belief in Conspiracy Theories

Belief in conspiracy theories has often been associated with a biased perception of randomness, akin to a nothing-happens-by-accident heuristic. Indeed, a low prior for randomness (i.e., believing that randomness is a priori unlikely) could plausibly explain the tendency to believe that a planned deception lies behind many events, as well as the tendency to perceive meaningful information in scattered and irrelevant details; both of these tendencies are traits diagnostic of conspiracist ideation. In three studies, we investigated this hypothesis and failed to find the predicted association between low prior for randomness and conspiracist ideation, even when randomness was explicitly opposed to malevolent human intervention. Conspiracy believers’ and nonbelievers’ perceptions of randomness were not only indistinguishable from each other but also accurate compared with the normative view arising from the algorithmic information framework. Thus, the motto “nothing happens by accident,” taken at face value, does not explain belief in conspiracy theories.

Distinct contributions of Brodmann areas 1 and 2 to body ownership

Although body ownership--i.e. the feeling that our bodies belong to us--modulates activity within the primary somatosensory cortex (S1), it is still unknown whether this modulation occurs within a somatotopically defined portion of S1. We induced an illusory feeling of ownership for another persons finger by asking participants to hold their palm against another persons palm and to stroke the two joined index fingers with the index and thumb of their other hand. This illusion (numbness illusion) does not occur if the stroking is performed asynchronously or by the other person. We combined this somatosensory paradigm with ultra-high field functional magnetic resonance imaging finger mapping to study whether illusory body ownership modulates activity within different finger-specific areas of S1. The results revealed that the numbness illusion is associated with activity in Brodmann area (BA) 1 within the representation of the finger stroking the other persons finger and in BA 2 contralateral to the stroked finger. These results show that changes in bodily experience modulate the activity within certain subregions of S1, with a different finger-topographical selectivity between the representations of the stroking and of the stroked hand, and reveal that the high degree of somatosensory specialization in S1 extends to bodily self-consciousness.

My face through the looking-glass: The effect of mirror reversal on reflection size estimation

People tend to grossly overestimate the size of their mirror-reflected face. Although this overestimation bias is robust, not much is known about its relationships to self-face perception. In two experiments, we investigated the overestimation bias as a function of the presentation of the own face (left-right reversed - as in a mirror - or nonreversed - as in a photograph), the identity of the seen face, and prior exposure to a real mirror. For this we developed a computerized task requiring size estimations of displayed faces. We replicated the observation that people overestimate the size of their mirror-reflected face and showed that the overestimation can be reduced following a brief mirror exposure. We also found that left-right reversal modulates the overestimation bias, depending on the perceived faces identity. These data underline the enhanced familiarity of left-right reversed self-faces and the importance of size perception for understanding mirror reflection processing.

Experience-based auditory predictions modulate brain activity to silence as do real sounds

Interactions between stimulis acoustic features and experience-based internal models of the environment enable listeners to compensate for the disruptions in auditory streams that are regularly encountered in noisy environments. However, whether auditory gaps are filled in predictively or restored a posteriori remains unclear. The current lack of positive statistical evidence that internal models can actually shape brain activity as would real sounds precludes accepting predictive accounts of filling-in phenomenon. We investigated the neurophysiological effects of internal models by testing whether single-trial electrophysiological responses to omitted sounds in a rule-based sequence of tones with varying pitch could be decoded from the responses to real sounds and by analyzing the ERPs to the omissions with data-driven electrical neuroimaging methods. The decoding of the brain responses to different expected, but omitted, tones in both passive and active listening conditions was above chance based on the responses to the real sound in active listening conditions. Topographic ERP analyses and electrical source estimations revealed that, in the absence of any stimulation, experience-based internal models elicit an electrophysiological activity different from noise and that the temporal dynamics of this activity depend on attention. We further found that the expected change in pitch direction of omitted tones modulated the activity of left posterior temporal areas 140–200 msec after the onset of omissions. Collectively, our results indicate that, even in the absence of any stimulation, internal models modulate brain activity as do real sounds, indicating that auditory filling in can be accounted for by predictive activity.

Doubles Everywhere: Literary Contributions to the Study of the Bodily Self1

The topic of the double is a hallmark of romantic, gothic, and fantastic literature. In the guise of the second self, the alter ego or the doppelgänger, fictional doubles have long fascinated critics, clinicians, and scientists. We review classical approaches to the theme and propose a broad clinical and neurocognitive framework from which to examine major instances of the motif in literature. Based on neurological disorders of the bodily self (including unilateral and whole body illusions and duplications), as well as related experimental approaches, we provide examples of literary depictions of bodily fragmentation and splitting; autoscopic hallucinations; the classical doppelgänger, second self, or heautoscopic double; the feeling of a presence; out-of-body experiences; and so-called near-death experiences. Examples include works from Guy de Maupassant, E.T.A. Hoffman, Edgar Allan Poe, Robert Louis Stevenson, Fyodor Dostoevsky, Rudyard Kipling, and others. We discuss these literary cases of doubles from a neurocognitive perspective, and suggest that common mechanisms of the bodily self are involved in the emergence of pathological illusory doubles, literary creations of the double, as well as widespread cultural and religious beliefs about the existence of doubles and the soul.

Visconti and Fellini: From Left Social Neorealism to Right-Hemisphere Stroke

The acclaimed Italian directors Luchino Visconti and Federico Fellini had very different life trajectories that led them to become major figures in the history of cinema. Similarities, however, can be found in their debuts with the neorealist genre, their personalities, creative styles and politicocultural involvement, and ultimately in the neurological disease that struck them at the end of their careers. Both suffered a right-hemispheric stroke that left them hemiplegic on the left side. We review their life and career to put that event into perspective, and then discuss its aftermath for both artists in the light of our current knowledge of right-hemispheric functions. Visconti showed a tremendous resilience following the accident and managed to direct several films and plays as an infirm, whereas Fellini had to put an end to his career but still was able to display his talents to the neuropsychologists that treated him. A speculative account is given of the links between right-hemispheric symptomatology and the premorbid personality of these highly prolific patients.