neurobiology of consciousness

consciousness

• arousal

• awareness of self/environment + motivation to respond

arousal

global state of wakefulness

• stage 3 non-REM sleep to high vigilance

awareness

ability to perceive one or more specifc stimuli

• Visual

• Tactile

• Auditory

• Gustatory

• Olfactory

• Vestibular

• Proprioceptive

• Interoceptive

motivation

the drive to act on stimuli, both internal and external, that have entered conscious awareness

reticular formation

• Wakefulness

• Eye movements

• Swallowing/vomiting

• Posture/locomotion

• Respiration

• Blood pressure

• Sensory awareness

ascending arousal system

networkk of neurons that project to multiple brainstem source nuclei from within and next to RF to the cortex through thalamic and extrathalamic pathways

• network is complex and diffuse

thalamic pathway

starts in RF, projects to thalamus then spreads out to cortical regions

extrathalamic pathway

RF to thalamus but mainly bypassing the thalamus. then hypothalamus, basal forebrain to cerebral cortices

thalamic specific fibers

• both are cholinergic

• pedunclulopontine tegmental nuclei (PPT)

• lateraldorsal tegmental nuclei (LDT)

how does one become aware of stimuli

• Conscious awareness and arousal states interact

• No arousal: no awareness

• High arousal? Awareness can focus on one modality at expense of others

• Interactions between the cortex and specific and nonspecific thalamic nuclei (e.g., reticular, intralaminar)

ascending reticular activating system

originates in teh reticular formation, projections activate the cerebral cortex via glutamtergic relays in the thalamus

thalamus

• Relay station and filters and modulates information

  • Coordinates activity in widespread areas

• Cortico-striatopallidal-thalamocortical loops

• Cortico-thalamocortical loops

frontal/parietal systems

function is movement planning/execution

Frontal eye fields (FEF)

Supplementary motor area (SMA)

Anterior cingulate cortex (ACC)

Posterior parietal cortex (PPC)

arousal systems

Basal forebrain (BF) and

brainstem cholinergic (LDT/PPT)

Locus ceruleus (LC)

Mesencephalic reticularformation (MRF)

brainstem attention capture mechanism

redirects attention to peripheral sensory inputs

Pretectum (PT)-OKN

Cerebellar/vestibular orientation (VOR)

Acoustic startle (ASR)

Tendon somatosensory feedback afferents

Nociceptive afferents

Postural reflexes

thalamus interactions with striatum

strong and largest efference to striatum

• provides connection to large cerebral networks: potential mechanism for translating sensory/motor activity to awareness

resting state networks

• connnectomes

• default mode

connectomes

spontaneous resting brain activity, functionally connected brain regions

default mode

what happens in your brain when you stop thinking about everything

pathophysiology of disorders of consciousness

slide 24

five basic wave forms

1. gamma

2. beta

3. alpha

4. theta

5. delta

6. frequency is the key characteristic

alert wakefulness

• Alpha waves (8–13 Hz, more posterior, prominent with EC and/or relaxation)

• Beta waves (13–30 Hz, more anterior, prominent with mentation)

• Gamma waves (more than 30 Hz, information processing during a cognitive task)

decrease in cortical arousal

• Theta waves (4–7 Hz, drowsy)

• Delta waves (less than 4 Hz, highest amplitude; deep, dreamless sleep: stages 3–4)

sleep wake cycle and EEG activity

• alpha = awake

• beta = REM sleep

• theta = stage 1

• delta = 2-4

sleep is 1/3 of life

• Suprachiasmatic nucleus of hypothalamus

• Reduced motor activity

• Decreased response to stimulation

• Relatively easy reversibility

Suprachiasmatic nucleus of hypothalamus

• Regulates circadian rhythm

• Melatonin released from pineal gland

• Light inhibits release of melatonin

• GABA inhibits neurons involved in wakefulness

Monoaminergic

• Maximum activity during wakefulness

• Decrease during non-REM sleep

• Almost zero activity during REM sleep

• Similar to motor neurons

• Dopaminergic activity patterns

Cholinergic

Difference from monoaminergic: activity increases during REM sleep

Sleep-Wake Cycle Neural Activity

Monoaminergic (NE, 5HT, Hist)

Cholinergic (Ach)