NEURAL CORRELATES OF CONSCIOUSNESS NBEE 5700 Introduction to

NEURAL CORRELATES OF CONSCIOUSNESS NBE-E 5700 Introduction to Cognitive Neuroscience Anastasia Lowe 9. 2. 2016

“The minimal set of neuronal events and mechanisms jointly sufficient for a specific conscious percept” - Koch or more simply. . A neural system N is an NCC if the state of N correlates directly with states of consciousness.

• WHAT IS CONSCIOUSNESS? Creature consciousness (being conscious) • Background state of consciousness • • awake, asleep, under hypnosis Contents of consciousness (specific states of consciousness)

HOW TO SEARCH FOR AN NCC? • How to measure consciousness? • Some models for the identity of an NCC include: • The 40 Hz theory of consciousness • Neural assemblies bound by NMDA • NCC for visual consciousness in the visual cortex • …and many more

VISUAL CONSCIOUSNESS Blindsight • Damage in the primary visual cortex —> prevents visual stimuli from reaching the primary visual cortex —> no conscious visual experience • Secondary visual pathway until superior colliculi • An NCC for visual consciousness somewhere in the primary visual cortex?

VISUAL CONSCIOUSNESS Binocular rivalry • When two different images are presented to the two eyes simultaneously, you are conscious of only one image at a time. —> dominance switches Logothetis et al. studied this in monkeys • They were presented two different images to which they responded by pressing bars • Cortex monitored with electrodes • Primary visual cortex didn’t correlate with cell firing

VISUAL CONSCIOUSNESS CASE 2 • Faces & vase tagged with noise that oscillated at different frequencies • Allowed tracking of EM activity of human visual cortex associated with percept of face and vase. —> visual cortex activity followed self-reported observation of subjects • Thus, it was proposed that sensory cortex activity is associated with conscious percepts.

THE 40 HZ THEORY OF CONSCIOUSNESS • Francis Crick and Christof Koch suggest that consciousness depends on shortterm memory and on some sort of attentional mechanism. —> sets the neurons to fire in a semioscillatory way, around the frequency of 40 -70 Hz. —> oscillations give rise to short-term memory. • Normal brain activity between 8 and 100 Hz. • During passive activity around 8 -30 Hz, during a coma close to 0 Hz. • Alert and active —> neural oscillations of around 40 Hz. How do neurons oscillate when we think or perform tasks? • Animals were trained to respond to objects based on either their color or orientation • Brain activity measured in the prefrontal cortex, where working memory is located • Neuron oscillations in synchrony with task that was being completed • Also found that the brain uses lower- frequency brain waves to inhibit neurons when they are not needed.

• NEURAL ASSEMBLIES BOUND BY NMDA Prior to surgery patient undergoes anaesthesia conscious —> unconscious • Anesthetics works by interfering with the NMDA receptors • Hans Flohr observes that functional NMDA receptors are required for consciousness • Deductive reasoning would have us think NMDA receptors are the NCC for consciousness

TO END THIS… • Finding an NCC does not mean we will understand the processes underlying consciousness. • However, once know which systems are NCCs, it will enable us to research the mechanisms by which they work, and how they produce various characteristic functional effects.

SOURCES AND FURTHER READING • Jääskeläinen, Iiro. An Introduction to Cognitive Neuroscience. • Chalmers, David. “What is a Neural Correlate of Consciousness? ” • Parkkonen et al. “Early visual brain areas reflect the percept of an ambiguous scene. ” • Buschman, Timothy et al. “Synchronous Oscillatory Neural Ensembles for Rules in the Prefrontal Cortex" • Blake et al. “Can binocular rivalry reveal neural correlates of consciousness? ” • Crick, Francis, and Koch, Christof. “Towards a neurobiological theory of consciousness. ” • Carter, Olivia. Binocular rivalry.