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Higher CNS - functions

Peter Århem

Department of Neuroscience

Organisation of the human brain

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Three anatomical levels Neocortex – limbic system - basal ganglia

Three evolutionary levels • Neocortex – advanced mammals • Limbic system – primitive mammals • Basal ganglia - reptiles

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Three levels of behaviour Instincts - emotions – abstract thinking

Emotions - the limbic system

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• Olfactory

cortex

• Gyrus cinguli

• Amygdala

• Hippocampus

• N. accumbens

Integrated circuit – The limbic system

Hippocampus – consolidation of memories

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Amygdala – fear and aggressiveness Connected to gyrus cinguli, thalamus, hypothalamus

Thalamus

Nucleus accumbens and mesolimbic system – pleasure and reward

• Mesolimbic pathway between ventral tegmental area and n. acumbens

• Dopaminergic pathway

Mesolimbic pathway

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Monoamine pathways – complex emotions

Nucleus accumbens and sexuality

• High dopamine levels in monogamous voles (prairie vole) • Low dopamine levels in polygamous voles (montane vole)

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Nucleus accumbens and drug addiction

• Nucleus accumbens is the addiction center of the brain

• Dopamine, but also noradrenalin and serotonin, are key transmitters

• Drugs as nicotine, opiates and cocaine increase release av dopamine

Sleep – the reticular activating system

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• Vital process – from fruitfly to man

• Different EEG rhythms

• Regulated by reticular activating system

Sleep

Slow wave sleep and REM-sleep

• Slow wave sleep - 80% of sleep time,

lowered metabolism, respiration, muscle tonus, heart frequency, body temperature

• REM-sleep (dream sleep) - 20% of sleep time, 10-40 min periods, rapid eye movements

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Sleep and wakefulness

Beta waves 15-30 Hz Alpha waves 8-15 Hz Theta waves 4-7 Hz Delta waves 1-4 Hz

Gamma waves 40-50 Hz

Sleep stages during night

Night hours

Light slow wave sleep

Deep slow wave sleep

Awake

REM sleep

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Wakefulness regulated by reticular activating system (part of formatio reticularis in brain stem)

via thalamus

Sleeplessness: • Problems with concentration, learning and memory • Increased frequency of infections and depressions • Increased appetite Suggested hypotheses: • Consolidation of memory? • Adaptation to day-life?

Why do we need sleep?

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Cognition – neocortical association areas

Cognition

Set of mental abilities and processes related to

• knowledge,

• attention,

• memory,

• judgement and evaluation,

• reasoning and computation,

• problem solving and decision making,

• comprehension and production of language,.…

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Association areas

• Limbic association cortex – temporal and gyrus cinguli • General sensoric association cortex – parietal–temporal-occipital • Prefrontal association cortex - frontal

Prefrontal association cortex and personality – The case of Phineas Gage

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The prefrontal association area and personality

• Moral, intelligence, self- discipline, social competence, ”right & wrong”

• Controls basic instincts

• Left side: optimistic

• Right side: pessimistic

Speech areas in the left hemisphere • Wernicke’s area (sensory) • Broca’s area (motor)

Wernicke,s area

Gyrus angularis

Fasciculus arcuatus

Broca’s area

• Heard speech - Wernicke’s area – Fasciculus arcuatus – Broca’s area – speech • Seen text – Gyrus angularis – Wernicke’s area – Fasciculus arcuatus - Broca’s

area - speech

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Aphasias • Wernickes area (sensory aphasia) Fluent speech; nonsense words • Brocas area (motor aphasia) Fragmented speech; well-preserved comprehension

Dyslexia

• Difficulties in reading and writing

• 10-20% of children

• Low activation in Wernicke’s area and

Gyrus angularis

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Lateralization

Relation between hemispheres

• Contralaterality

– Right hemisphere controls left body half

– Left hemisphere controls right body half

• Corpus callosum

– Connects left with right hemisphere

– Enables communication between left and right hemispheres

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Hemispheric specializations

Left side:

• Speech and language

• Analytic, arithmetic

• Perception of time

Right side:

• Patterns

• Spatial perception

• Context

Summarizing questions

1. EEG rhythms in an awake person (with closed and open eyes)? 2. Which nucleus is central in the reward system of the brain? 3. Which brain system regulates emotional reactions? 4. A nucleus that is activated at emotions of fear? 5. Which diencephalic group of nuclei is the main relay station for sensory information? 6. In which hemisphere do we ususally find the speech areas? 7. Which hemisphere handles spatial information best? 8. Some functions related to activity in the frontal lobe?