Lecture 23 - Higher brain functions

What is consciousness typically defined as?

Being alert, aware, and able to respond immediately to environmental cues.

Why is consciousness called the “hard problem” of neuroscience?

Because it is difficult to define neurophysiologically and requires not only awareness but also self-awareness, which allows reflection and planning.

Which brain functions are thought to be required for consciousness?

Processing across multiple brain regions.

What are the main states of consciousness?

Conscious (awake, responsive), altered (e.g., sleep), vegetative (wakefulness without awareness), and coma (no wakefulness or awareness, no sleep-wake cycle).

How is sleep defined in terms of consciousness?

A reversible brain state where one can be roused but is typically unaware of surroundings

What characterizes a coma?

No wakefulness or awareness, no sleep-wake cycle, and no response to external stimuli; often caused by cortical or brainstem dysfunction

What is a vegetative state, and when is it “persistent”?

A state with sleep-wake cycles and autonomic functions intact but no awareness or cognition. Persistent if lasting more than 4 weeks.

What are hallucinations, and how do they differ from dreams?

Hallucinations are wakeful perceptions without external stimuli, while dreams occur during sleep.

In which sensory modalities can hallucinations occur?

Vision, sound, taste, smell, and others.

What causes hallucinations at the brain level?

Activation of sensory-processing brain regions without normal external input.

What psychiatric disorder is strongly associated with hallucinations and disordered thinking?

Schizophrenia.

Define psychosis.

A difficulty distinguishing between what is real and not real.

What are common symptoms of schizophrenia?

Hallucinations, delusions, paranoia, disorganized thought, social withdrawal, and apathy.

What percentage of people are affected by schizophrenia, and in which sex is it more common?

About 0.5% of people; more common in males.

What neurotransmitter system is overactive in schizophrenia?

The dopamine system.

Which drugs can trigger schizophrenia-like psychosis, and how?

Amphetamines and cocaine, by acting on dopaminergic pathways.

Which class of drugs is effective in treating schizophrenia symptoms?

D2 dopamine receptor blockers

What factors contribute to schizophrenia risk?

Genetic (~75%), developmental (e.g., prenatal malnutrition, oxygen deprivation), and environmental (e.g., social deprivation)

How is sleep defined neurophysiologically?

Suspension of normal consciousness with a distinct pattern of brain activity

What are some proposed functions of sleep?

Restoration of homeostasis, conservation of energy, synchronization with light-dark cycles, and memory consolidation

What are consequences of sleep deprivation in humans?

Reduced immune function, poor memory, short attention span, emotional instability, increased blood pressure, fatigue, and ultimately death.

What are the two main drivers of the sleep-wake cycle?

Homeostatic drive and circadian drive.

What is the homeostatic sleep drive, and what molecule is key to it?

The build-up of “sleep pressure” during wakefulness; partly due to adenosine accumulation, which inhibits CNS activity.

How does caffeine promote wakefulness?

By blocking adenosine receptors.

What brain structure controls circadian rhythms as the “master clock”?

The suprachiasmatic nucleus (SCN).

Define circadian rhythm in one sentence

A rhythmic change persisting near a 24-hour cycle even without external cues.

How does the circadian transcriptional feedback loop work?

Clock genes are transcribed into RNA, translated into proteins, and these proteins inhibit their own transcription, creating an oscillatory cycle.

What is the average human free running circadian rhythm?

About 24.2 hours.

What are zeitgebers, and give an example.

External cues that reset biological clocks; e.g., light or food.

Who pioneered chronobiology and discovered freerunning rhythms?

Jürgen Aschoff.

What is jet lag, and what causes it?

A disruption of circadian rhythms due to rapid travel across time zones, desynchronizing SCN and peripheral clocks

What are common symptoms of jet lag?

Sleep disturbances, daytime sleepiness, poor concentration, digestive issues, and mood changes.

Why is it harder to travel eastward than westward?

Because humans have a freerunning rhythm slightly longer than 24 hours, so it is easier to lengthen the day than shorten it.

What is social jetlag?

A mismatch between an individual’s internal circadian rhythm and social schedules (e.g., work or school).

What health condition has social jetlag been linked to in the Dunedin study?

Metabolic syndrome.