Integrated function

Cerebral cortex

  • Voluntary movement
  • Language
    • Language area= left hemisphere
    • Wernicke’s area
      • superior & posterior portion of the temporal lobe
      • LANGUAGE COMPREHENSION
        • comprehension of written words, sounds, signs
      • Wernicke’s aphasia
        • can speak, but makes no sense
        • eg. says “chicken’ when pictures of chairs
    • Broca’s area
      • Frontal lobe
      • LANGUAGE EXPRESSION
        • speak/write word
      • Broca’s aphasia
        • can comprehend, but cannot speak
        • Can identify trees,  chairs etc but cannot say it
  • Emotions & motivation
    • 4 components
      • Cognition
      • Affect (feelings)
      • Conation (urge to take action)
      • Physical changes (BP, HR changes, sweating)
    • Inputs from
      • Memory
      • Special senses
    • Relayed in
      • Limbic cortex
      • hypothalamus
    • Anger & Aggression
      • Cerebral cortex
      • limbic system
      • hypothalamus
    • Fear & Anxiety
      • Amygdala
    • Motivation
      • impulse that drives our action
      • Physiological changes/pleasure derived from stimulation of “pleasure centres” which activate dopaminergic neurones
      • Reward/ Approach system
        • Cocaine appears to act here
      • Avoidance associated with lateral portion of posterior hypothalamus, dorsal midbrain & entorhinal cortex
        • punishment/ avoidance system
  • Sleep
  • Learning & Memory
    • Learning: acquisition of new memory/skills
    • Memory: retention of information/skills/thoughts
    • 2 types of learning
      • Associative
        • Connections between two or more stimuli
        • eg. Conditioned Reflexes (Pavlov’s dogs)/use of mnemonics/learning hands-on that fire is hot
      • Non-associative
        • Repetition
        • Habituation
          • reduced responses to repeated stimuli
        • Sensitisation
          • increased response
        • Habituation/ sensitisation
          • depends on how important it is to us
          • eg. a mother sleeps through loud noises but wakes up at her baby’s cry
    • 2 types of memories
      • Non-declarative, implicit, reflexic
        • Memory of learned skills ( & habits)
          • eg. riding a bicycle/route to home
        • Simple classical conditioning
        • Priming
        • Stored in several areas including
          • Cerebellum
          • Basal nuclei
          • Pons
        • Once learnt, do not require a conscious effort of recall
      • Declarative, explicit
        • Memory of learned experiences
          • facts or figures
          • eg. recite the alphabet, remember birthdays
        • Short-term memory
          • consolidated into long-term memory
          • in hippocampus (encoding in HIPPOCAMPUS)
        • Long-term memory stored in
          • various parts of the neocortex
          • stimulation of implanted electrodes plays back memories
        • Amygdala add emotional colour to memories
    • Areas of the brain associated with memory
      • Working/short term memory
        • frontal lobe
      • Long term memory
        • hippocampus
      • Habits & skills
        • cerebellum
        • basal nuclei

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Cerebral lobes

  • Damage to frontal lobe
    • reduced anxiety
    • personality changes
      • unpredictable
      • uninhibited social behaviour
    • epilepsy
  • Damage to parietal lobe
    • Agnosia
      • Loss of cognition
      • No sensory deficit
        • but fails to recognise objects
        • Visual Agnosia
          • can recognise through touch but not by vision
        • Astereognosis
          • cannot recognise by touch
    • Apraxia
      • loss of ability to perform specific purposeful movements
        • cannot wave goodbye, but can perform that act spontaneously
      • Constructional apraxia
        • Failure to use everyday objects appropriately or construct/draw a simple object
      • Kinetic apraxia
        • Deficit in the control of movements of one hand caused by damage to the premotor area of the frontal lobe of the opposite side
    • Neglect syndrome
      • stroke in posterior region of right hemisphere
      • cannot perform left hand side functions

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Limbic system (Rhinencephalon)

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  • Rim of cortical tissue around the hilum of the cerebral cortex and associated deep structures (amygdala, hippocampus & septal nuclei)
  • Plays a role in
    • ANS functions
    • Olfaction
    • Feeding behaviour
    • Sexual behaviour
    • Rage & fear
    • Motivation
  • Principal connections of limbic system
    • Hippocampal system
      • hippocampus-fornix-mamilary body- ant.thalamic nuclei- cingulate cortex- hippocampus
    • Olfactory & amygdaloid connections

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Memory

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Encoding (of memory)

  • Not known how
    • Repetition
    • How important it is to you also counts
      • eg. you get married only once, but remember the date
  • Short -term memory
    • stored in the frontal lobe but only temporarily (a few seconds to a few minutes) 
    • the information needs to be consolidated into long-term memory
      • because the space is limited
  • Long-term memory
    • resides in the hippocampus
    • lasts years/ lifetime
  • Forgetting is an essential part of learning
  • Cases of herpes simplex attacking the brain
    • hippocampus
  • Brain surgery performed to relieve epileptic seizures
    • very short memory span
    • but can recall long-term memories

Long term potentiation (LTP)

  • Because of the property of plasticity
    • ability to alter the anatomy and function in response to changes in its activity patterns
    • new neurons are produced in the areas involved in memory
  • Long term potentiation
    • repeated stimulation results in increased strength of that synaptic connection
      • increased number of EPSPs
      • Brief patterned stimulation leads to a long-lasting increase in the efficacy of synaptic transmission lasting minutes to hours!
    • Memory improves with repetition
  • First seen in hippocampus (encoding)
    • Consolidation of long-term memory

Conditioned reflexes

  • Reflex response to a stimulus that previously elicited no response
    • by repeatedly pairing the stimulus with another stimulus that normally produces the response
      • Eg. Salivation (response) occurs when meat is placed in the mouth
        • Unconditioned stimulus (US)
      • Ringing of bell which normally does not cause salivation
        • conditioned stimulus (CS)
        • before placing the meat in the mouth
      • Repeatedly doing this results in salivation when the bell is rung
  • US combined with pleasant or unpleasant effect helps to establish the conditioned reflex
    • Positive & Negative reinforcement
  • If the CS is presented repeatedly without US
    • the conditioned reflex eventually dies out
      • Extinction/Internal inhibiton
  • Operant conditioning
    • taught to operate the environment to obtain a reward or avoid punishment
      • CS is a light or other signal that alerts the animal to perform a task
      • US is the pleasant or unpleasant event
        • eg. light- electric shock
        • can be prevented by pressing a bar

Circadian rhythm

  • Rhythms < 24 hours- ultradian
    • e.g. heart beat, respiratory cycle
  • Rhythms > 24 h – infradian
    • e.g. menstrual cycle, gestation
  • Peripheral clocks/rhythm generators
    • exist in many tissues
    • but the ‘master clock’ is the suprachiasmatic nucleus (SCN)
  • Circannual rhythms
    • yearly rhythm
    • e.g. breeding, hibernation, migration
  • Endogenous Rhythms
    • dictated by the “Biological Clock”
      • suprachiasmatic nucleus (SCN)
    • But influenced by exogenous cues
      • Entrainment by social and physical cues
  • Pineal gland produces melatonin in the dark
    • drowsiness, loss of alertness
    • Useful to minimise
      • Jet lag 
      • Seasonal Affective Disorder in winter

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