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Hemispheric specialisation

  • Left and right sensory and motor functions are separated into right and left hemispheres
    • Vision: left field of vision in both eyes goes to right side and visa-versa
      • Experiment involving those with the corpus callosum severed
      • If you had one hemisphere dedicated to one eye, then you'd have redundancy, so we have it wired so that halves of the visual field are processed in different hemispheres
        • Speech is located in the left hemisphere, so the word that the left hemisphere sees (the right field of vision) is spoken
    • Many functions are specialised to the left and right field, however
      • Language, calculation is not found in both hemisphere because it is a new function (only in left brain)
      • Right hemisphere has spatial abilities, simple language, comprehension, nonverbal ideation
      • However, in the same experiment above, if the person has to pick up an object, they may get it right – can understand, but not speak
  • The corpus callosum allows the brain to seamlessly share information from left side to right side
  • Sperry and Gazzaniga performed above experiment with split CC (this is used to treat epilepsy, where there is too much excitability; nowadays we have medications, or we just excise the hyperexcitable part of the brain, or just severe the anterior 2/3 of CC)
    • They found that the two halves of the brain act autonomously; the patient can draw with two hands separately at once. Also, if he sees on one side of his vision one word and another word on the other side, he would draw one word, and not be able to say it, and say another word. The drawing communicates between the two sides of the brain and allows him to draw it. Like, honestly, WTF?!
      • His right hemisphere cannot simplify things down into easy ideas, his drawings are all 3D imitations of everything
      • Different personalities: one side of the brain wants to be an accountant while the other one wants to be a racing car driver
    • His main brain is is left brain which he talks with and uses to interact with the world
      • Ie: in one person, one side of the brain wanted to be an accountant, the other a race-car driver
    • This operation is still performed, but the latter 1/3 spared

Insert table

  • Control of speech:
    • Language
      • Centres lie between motor (face/head) and auditory cortex regions
      • Communication via arcuate fasciculus sends information from Wernicke's area to Broca's area, and this allows words to be formed physically; Broca's area allows fragments of words to be spliced together to make fluent speech. If you have Wenicke's area damaged, then you can think up thoughts, and say words well, but the structure of the language is weird and meaningless.
    • Knowledge of these areas depends on lesions studied

Aphasia.PNG

(NB: Anomic - can't think of the word when they have to find it themselves: no dictionary function. They can repeat words, though).

  • Path of the language areas:
    • The primary auditory cortex detects pitch/intensity/location of sound
    • Wernicke’s area translates the sounds/patterns into words and allows us to put words together
      • This connects to the Broca’s area by the arcuate fasciculus
    • Broca’s area controls the mechanical aspects of speech production allowing us to form words
  • Damage to various areas and their effect (types of aphasia):
  • Note:
    • With Wernicke’s aphasia, the person can learn to speak again, Broca’s they can’t
    • This is a simplified table, speech also involves the thalamus, basal ganglia and additional surrounding cortex
  • If these are affected, it is unlikely the patient will recover speech
  • Other type of language are also affected since they use similar pathways
    • Eg: written word
  • Sign language is also effected by lesions to the Wernicke and Broca's areas.
  • Using neuroplasticity, people who have had strokes can then learn to speak using alternate pathways.

Types of recordings

  • Scans:
    • ECG – electrocardiogram
    • EMG – electromyogram (muscle)
    • EEG–electroencephalogram(cortex)
      • These are ‘mass scans’ – they measure the whole electrical change not single cells
  • EEG
    • Made from outside the scalp
      • The meninges, skull etc dampen the signal
    • In one mm3, there are 10 000 neurons, thus it is hard to individualise neurons and if they are not coordinated, we get static
      • Thus, we can only see something on EEGs when neurons are active all at once
    • Brain waves are pretty small until all the brain waves are synchronised (e.g. seizure)
  • Each line represents a different electrode
    • Petit mal seizures can create a large EEG signal due to synchronised cell firing
      • These can be measured and the information used to locate the focus of an epileptic seizure

Sleep

  • As we fall asleep, our brain activity becomes synchronised
  • Definition – a reversible behavioural state of perceptual disengagement from and unresponsiveness to the environment; primarily a function of the brain and not of other organs (hence it affects brain performance)
    • There are 3 physiological behavioural states in man and other mammals
      • Wake
      • Non-REM sleep
      • REM sleep
    • Awake vs sleep – difference is in the activity in the cerebral cortex, other systems are unaffected (can't determine state without examining the brain)
  • Sleep can be monitored using different polygraphs (done in sleep studies):
    • EEG–electroencephalogram (brainwaves)
    • EOG – electrooculogram (eye movements)
    • EMG – electromyogram (muscle tension – of the jaw)
  • Wake: EEG – desynchronised, EMG – variable; because we have lots of little waves corresponding to thoughts; each AP is quite small; lack of synchrony means waves aren't large
  • Non-REM (stages 3-4): EEG – synchronised, EMG – attenuated but present
  • REM: EEG – desynchronised, EMG – absent (active paralysis)


EEG, EOG and EMG of sleep

  • Drowsy: 10cycles/s (alpha waves)
  • Stage 1: theta waves (3-7 cycles/s)
  • Stage 2: 12-14 cycles per second - sleep spindles and K complexes
  • Delta sleep: 1cycle/s, epileptic-like pattern (synchrony)
  • Top: awake and relaxed
    • Alpha activity (present in 50% of the population)
    • Slow rolling eye movements of eye blinks in EOG
    • Relatively high submental EMG tone
  • Middle: non-REM stage 4 (deep sleep)
    • Delta EEG activity in >50% of the population
    • EOG leads mirror all the Delta EEG activity – synchronised
    • Submental EMG activity is slightly reduced
  • Bottom: REM sleep
    • Rapid eye movements
    • Mixed frequency EEG
    • Low submental movement – paralysed, motor output is switched off

State: non-REM stage 4 (deep sleep)

  • Note: eye leads mirror what is happening in the brain
  • EEG activity becomes synchronise
  • EMG is small but not absent

State: REM sleep

  • Rapid, abrupt changes in eye movements
  • EEG activity is much smaller, not synchronised
  • EMG is absent
    • Paralysis stops you from moving during sleep (so we aren't hurt)

Control of sleep

  • Reticular formation is important (in brainstem/midbrain)
    • Made up of nuclei and extends through the brainstem and midbrain
    • Important in the sleep/wake cycle
    • Projects to the thalamus and in this way regulates the cortex
      • Also has spinal cord projections to regulate motor activity
    • Uses NTs (neuromodulator neurotransmitters) like NA, 5HT, ACh and thus has diffuse effects
      • ACh neurons have 250 000 synapses, vs 10000 in glutamate synapses, thus more diffuse
  • RF is driven by centres like the suprachiasmic nucleus of the hypothalamus (above the optic chiasm) that control the circadian rhythm (sleep/wake cycle in line with the daytime of the outside world)
    • This gets input from photoreceptive ganglion cells that use melanopsin – synchronises sleep/wake with night/day cycles (you can use melatonin OR early morning sunlight to get this system to resynchronise your brain)
    • If we are cold when we wake up, the circadian rhythm has become uncouplaed
  • Ultradian rhythm – 90 minute cycle that is generated in the medulla (if lying in bed in the wrong part of the cycle, you should get up and do something quiet, have a hot drink or read a book, and when you feel drowsy, hop back into bed. Associate the bed with sleep, don't sit on your laptop in bed (oops))
    • This cycle is involved in alertness vs sleepiness – this is superimposed on the circadian cycle
  • See the table of neurotransmitters at different phases in the cycle

Alternation and consolidation

  • Why do we need sleep?
    • We don’t know
    • Possible to consolidate memory; if you study something before going to sleep, your memory of that information is better once you wake up
  • Consolidation requires an alternation between REM and non-REM sleep
    • In the deep sleep stages (non-REM), the hippocampus (short term memory) can control the cortical activity
    • Waking – sensory input affects the cortex which transmits to the hippocampus (hippocampus is very plastic; can remember stuff short term)
    • Slow wave sleep (non-REM) – hippocampus transfers information to neocortical cell groups’ (neocortex is less plastic; needs a few repetitions to remember something)
    • REM sleep – consolidation of information relayed from the hippocampus in the neocortex
  • REM sleep = drive hippocampus
  • Non-REM sleep = driving neocortex
  • Over the period of the night, your sleep becomes more shallow until you eventually awaken
  • Older people have less REM sleep, so they need less sleep overall