Neural correlates of consciousness

Summary

The neural correlates of consciousness (NCC) refer to the relationships between mental states and neural states and constitute the minimal set of neuronal events and mechanisms sufficient for a specific conscious percept. Neuroscientists use empirical approaches to discover neural correlates of subjective phenomena; that is, neural changes which necessarily and regularly correlate with a specific experience. The set should be minimal because, under the materialist assumption that the brain is sufficient to give rise to any given conscious experience, the question is which of its components are necessary to produce it. Neurobiological approach to consciousness A science of consciousness must explain the exact relationship between subjective mental states and brain states, the nature of the relationship between the conscious mind and the electro-chemical interactions in the body (mind–body problem). Progress in neuropsychology and neurophilosophy has come from focusing on the

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The ability to notice erroneous behavior is crucial for effective training. Within the framework of neuroprosthetics, numerous studies in electroencephalography (EEG) confirm the existence of neural correlates when humans perceive the erroneous actions of the device. Subsequently, the decoding of this correlate has been used to correct the erroneous behavior performed by the agent or to tune the behavioral strategy of the agent, among others. However, a main limitation of current approaches is that the actions of the agent were discretized, thus restraining the usability of such systems. The main objective of this PhD study is to study, and decode, the neural correlates of error evaluation under continuous trajectories performed by external agents; and to use this decoding to tune the continuous behavior of the agent for individual users. To accomplish this goal, two essential questions will be investigated: (i) whether it is possible to infer individual preference under continuous state-action scenarios, and (ii) how to create a reliable decoding pipeline in a continuous fashion. Results obtained during the first year of the PhD have confirmed the existence of such correlates under continuous motions of a robotic arm. Furthermore, such correlates encode individual preferences, indicating that the neural prosthesis can be also customized for individual users, which may play an important rule to increase the quality of brain-computer based assistance. This property not only will increase the level of perceived assistance provided by a brain-computer interface, but also may facilitate embodiment of the brain-controlled device.

EPFL2021

In the main part of this thesis, I investigate the neural correlates of nonretinotopic processing. We might intuitively think of the visual representation of the world as retinotopic, as is the case for the organization of most visual brain areas, but in fact our perception is usually not retinotopic. Consider for example a bicycle passing by with a reflector on one of its wheels. The reflector appears to move in a circular or prolate cycloidal orbit. It’s true motion trajectory, however, is a curtate cycloid. It seems that we perceive the reflector motion relative to the bicycle. The bicycle thus serves as a moving reference system for computing the motion of its constituent parts. Only little is known about the neural correlates of this type of non-retinotopic processing. Here, using EEG, I investigate the temporal dynamics of the encoding of non-retinotopic motion relative to a moving reference system. The results indicate that the motion of the reference system is discounted from the motion of the part already from 120 ms after stimulus onset and that the non-retinotopic representation dominates throughout the rest of the visual processing. Further, I use fMRI to show that the earliest area in the visual hierarchy holding non-retinotopic representations is the human motion processing complex (hMT+). In the second part of the thesis, the EEG correlates of light adaptation are investigated. Light adaptation is crucial for coping with the large range of ambient luminance values in our environment. We first confirm the known adaptation effect; the overall response to light flashes decreases substantially after adaption to bright light as compared to dim light. Furthermore, this adaptation effect depends on the wavelength of the light, being most pronounced for red light as compared to white, green and blue light. In addition, at short latencies (less than 100 ms) responses to light flashes are stronger after bright than after dim light adaptation for all colors except red. Our results show that even very short-latency EEG responses are differentially affected by different wavelengths of light.

EPFL2014

Out-of-body experiences (OBEs) are defined as experiences in which a person seems to be awake and sees his body and the world from a location outside his physical body. More precisely, they can be defined by the presence of the following three phenomenological characteristics: (i) disembodiment (location of the self outside one's body); (ii) the impression of seeing the world from an elevated and distanced visuo-spatial perspective (extracorporeal, but egocentric visuo-spatial perspective); and (iii) the impression of seeing one's own body (autoscopy) from this perspective. OBEs have fascinated mankind from time immemorial and are abundant in folklore, mythology, and spiritual experiences of most ancient and modern societies. Here, we review some of the classical precipitating factors of OBEs such as sleep, drug abuse, and general anesthesia as well as their neurobiology and compare them with recent findings on neurological and neurocognitive mechanisms of OBEs. The reviewed data suggest that OBEs are due to functional disintegration of lower-level multisensory processing and abnormal higher-level self-processing at the temporo-parietal junction. We argue that the experimental investigation of the interactions between these multisensory and cognitive mechanisms in OBEs and related illusions in combination with neuroimaging and behavioral techniques might further our understanding of the central mechanisms of corporal awareness and self-consciousness much as previous research about the neural bases of complex body part illusions such as phantom limbs has done.

Elsevier2005

EPFL2014