12. Arousal and Attention Systems

What is arousal?

A state of physiological activation and increased cortical responsiveness

What is alertness?

The state of being aware of and able to respond to stimuli

What system in the brain generates consciousness?

Ascending Reticular Activating System (ARAS)

What is the main function of the ARAS?

Maintains wakefulness, arousal, and cortical activation

Where does the ARAS originate?

Brainstem reticular formation

What are the main neurotransmitter-producing nuclei of the ARAS?

Locus coeruleus, dorsal raphe, VTA, PPN, parabrachial nucleus

What does the locus coeruleus release and where is it located?

Norepinephrine; posterior pons

Function of norepinephrine in ARAS from locus coeruleus?

Modulates alertness and attention, sleep-wake cycle

What does the dorsal raphe nucleus release and where is it located?

Serotonin; midline of midbrain, pons, medulla

Function of serotonin in ARAS from dorsal raphe nucleus?

Pain and mood regulation, circadian rhythm, attention

What does the posterior tuberomammillary hypothalamus release?

Histamine

Function of histamine in ARAS?

Promotes wakefulness and cognition

What does the pedunculopontine nucleus (PPN) release?

Acetylcholine

Function of acetylcholine from PPN and related nuclei in ARAS?

Wakefulness, cortical arousal, REM sleep

Which neurotransmitter is produced by the ventral tegmental area (VTA)?

Dopamine

Function of dopamine in ARAS?

Motivation, attention, arousal

Where does dopamine from VTA project?

Nucleus accumbens → prefrontal cortex

What brain structure is important for orientation and attention regulation?

Basal forebrain

Neurotransmitter used by basal forebrain for attention and orientation?

Acetylcholine

What happens in Alzheimer’s due to loss of basal forebrain acetylcholine?

Loss of attention and long-term memory

What cortical area regulates thoughts, behaviors, and emotion?

Anterior cingulate cortex

Damage to anterior cingulate cortex leads to what syndrome?

Akinetic mutism

What is akinetic mutism?

Alert but unable to move/speak, with reduced emotion and drive

What is the function of the dorsolateral prefrontal cortex?

Working memory and task shifting

Damage to dorsolateral prefrontal cortex causes what?

Perseveration (inability to switch tasks)

How does the ARAS receive sensory input?

From spinal cord, sensory pathways, thalamus, cortex

How does the ARAS project to the cortex?

Via thalamic intralaminar nuclei → cortex → increased alertness

Which hypothalamic nucleus regulates circadian rhythm via retinal input?

Suprachiasmatic nucleus (SCN)

What peptide is released from lateral hypothalamus to promote wakefulness?

Orexin

What are the main functions of the reticular formation?

Posture, tone, respiration, HR/BP, sleep-wakefulness