States of consciousness Prof. dr. Anton M.L. Coenen NICI – Department of Biological Psychology Radboud University Nijmegen The Netherlands

States of consciousness Lecture 1. Neural correlates of consciousness

Consciousness Complete set of mental facilities of an individual, expressed in awareness of what he is doing and what is happening. Consciousness represents the critical reactivity, analysing and evaluating incoming activity and preparing reactions.

Two types of consciousness Consciousness as experience Consciousness as the waking state

Consciousness as experience Being conscious of x (neural correlates of specific phenomenal content) (e.g. a green apple versus an orange apple)

Blackmore

Kolb

Blackmore

Mind and brain are different kinds of events (mental [B] versus physical [A] events) that exist independently but somehow interact and run parallel. THEORIES ON THE MIND-BODY PROBLEM Dualism AB

Monismthere is only one kind of events A=B materialism:only physical events (A) exist mentalism:only mental events (B) exist identity position: mental events (B) are the same as physical events (A), but described in different terms. Epiphenomalismmental events (B) occur during physical brain events (A), but are not caused by these events. They run in parallel but are autonomous and both are caused by a common underlying, mysterious, process (C) ACBACB

Objectivity Subjectivity: Qualia Conscious experience consists of qualia The smell of coffee The redness of red The beauty of music Dualism – monism – epiphenomenalism – materialism

Consciousness as the waking state Being conscious (neural correlates of the level of consciousness) States of consciousness

Consciousness is related to vigilance Synonyms: attention, alertness, arousal Alertness – Wakefulness – Drowsiness Sleep – Anaesthesia - Coma

Neural correlates of consciousness NCC (definition) A neural system N is an NCC if the state of N correlates directly with state of consciousness

NCC Consciousness is a gradual process related to the level of vigilance and the sleep-wake continuum. The electrical brain activity (EEG) reflects the level of consciousness.

Examples of Neural Correlates of Consciousness -Ascending reticular activating system (ARAS) (Reticular-thalamic activation system) -Intralaminar nuclei of the thalamus -The thalamo-cortical system -The cortical system -The electroencephalogram (EEG) and event-related potentials -40 Hz rhythmic activity in thalamo-cortical systems -The firing mode of thalamo-cortical neurons -Neurochemical levels of activations -Neural assemblies bound by NMDA

Measures: EEG (electrophysiology)

EEG Hans Berger (first recorded human EEG, 1928) Different EEG-bands (by frequency) Delta (0.5-4 Hz) - sleep Theta (5-7 Hz) - drowsy Alpha (8-12 Hz) - relaxed (eyes closed) Beta (13-22 Hz) - active Gamma (23-30 Hz) - very active

Measures: EEG Actively awake: beta and gamma Passively awake: alpha Drowsy: theta Light slow save sleep Deep slow save sleep

amplifier stimulus Stimulus onset Averaging Time-locked EEG Stimulus onset EEG EP

EP during wakefulness EP during sleep

Copyright restrictions may apply. Zeman, A. Brain : ; doi: /brain/ The pharmacologist's view of the activating system (from Robbins and Everitt, 1993; with permission--copyright 1993, MIT Press, USA): (A) shows the origin and distribution of the central noradrenergic pathways in the rat brain, (B) the dopaminergic pathways, (C) the cholinergic pathways, (D) the serotoninergic pathways

(After A. Bricolo, 1975)

Walter Rudolf Hess ( )Frédéric Bremer ( )

Giuseppe Moruzzi and Horace Magoun (1949)

Copyright restrictions may apply. Zeman, A. Brain : ; doi: /brain/ A schematic diagram of the reticular activating system, indicating pathways of activation which involve and those which bypass the thalamus

Hypocretinergic activity dependent on the states of consciousness. During wakefulness inputs converge on hypocretin neurons, activating noradrenergic neurons in the locus coeruleus, promoting arousal. During SWS, hypocretinergic activity decreases, but inhibition of REM-off neurons over REM-on cells is still effective. During REM sleep, hypocretin and REM-off cells are silent disinhibiting REM-on cells (after Sutchiffe and De Lecea, 2002)

Model of the neuronal network for reciprocal interactions between sleep and wake systems. Excitation is in green and inhibition in red, and black circles indicate areas for sleep. (after Fort et al, 2005)

Summary The concept of consciousness comprises two main types: consciousness as experience and consciousness as the waking state. Consciousness is present in the waking state, and absent or low in the sleeping state. The level of consciousness is related to the level of vigilance. States of consciousness are waking, drowsiness, sleeping, REM sleep and several altered states, such as coma, anaesthesia and hallucinations. States of consciousness are studied by the neural correlates of consciousness, such as the electroencephalogram (EEG), and the reticulo-thalamo-cortical system. The reticular formation in the upper brainstem regulates consciousness by the ‘ascending reticular activating system’ (ARAS). The ARAS activates the thalamo-cortical system by a dorsal glutamatergic pathway and a ventral cholinergic pathway. The low level of consciousness during sleep is induced by the GABAergic system located in the lower brainstem.