GETTING YOUR HEAD AROUND THE BRAIN

Palgrave Macmillan, October 2012

What do different parts of the brain do?CEREBRAL CORTEX

Frontal Lobe:Decision making, speech production, planning, movement

production, eye movements, smell and taste.

Parietal Lobe: Somatosensation, Spatial awareness, visual processing needed in action, numeracy

Temporal Lobe:Audition, Object recognition, face recognition, speech comprehension, memory (medial; hippocampus), emotion (medial)

Occipital Lobe: Vision

MEDIAL, MIDBRAIN AND OTHER STRUCTURES

Cingulate Cortex: Emotion, learning, memory

Diencephalon (thalamus, hypothalamus, pineal gland, pituitary gland):Homeostatic mechanisms

Brain stem (pons, medulla, substantia nigra, spinal cord, reticular activating system): Homeostatic mechanisms; sensory processing, movement

Cerebellum: movement control, balance, equilibrium

Basal Ganglia:movement control, procedural learning, emotional and cognitive functions.

What do different parts of the brain do?

The history of neuroscience- the recognition of the brain as the seat of the mind

Methodology in neuroscience

- imaging techniques (X-Ray, CT, PET, MRI, fMRI)

- listening techniques (single unit recording, EEG, ERP)

- neurostimulation (direct electrical stimulation, TMS, tDCS)

Chapter 1

Things to think about:

• If I wanted to understand how the brain comprehends the words we read, what methodology would I use? Why?

• What is your favourite methodology and what does it help us understand that no other does?

Chapter 1

What a neuron looks like and how action potentials happen

- neurons contain all of the organelles found in other cells in the body; these are contained in the cell body.

- motor neurons have the cell body at the top of the axon, sensory neuron cell bodies lie somewhere along the axon’s length.

Chapter 2

- the cell membrane is where the action potential happens. It is a phospho-lipid bilayer which contains ion channels to keep an imbalance between what is in the intra and extra-cellular fluid.

- the action potential happens via two mechanisms; the concentration gradient and the electrical gradient.- Potassium (K+) is more concentrated on the inside of the cell.- Sodium (Na+) is more concentrated outside of the cell.- Negatively charged proteins (or Anions, A-) and the free movement of potassium

means that the resting membrane potential is -65mv.

Chapter 2

- if the neuron is stimulated and the membrane potential reaches threshold (-50 mv), voltage gated Na+ open. Na+ rushes in down its concentration and electrical gradient making the inside of the cell more positive than the outside.

- voltage gated K+ then open and potassium rushes out, down its concentration and electrical gradient, making the inside of the cell less positive and more negative.

- The Na+/K+ pump restores the balance

Chapter 2

The synapse

- the action potential arrives at the axon terminal.- the depolarisation causes the influx of calcium (Ca++) which binds to synaptic

vesicles causing them to fuse with the terminal membrane.- the neurotransmitters released from the vesicles cross the synapse and binds to

post-synaptic receptors.

- Ion channels open directly or indirectly allowing an influx of excitatory (positive ions) or inhibitory (negative) ions into the neuron causing either EPSPs or IPSPs.

Chapter 2

Things to think about:

• What does an action potential look like graphically and why?

• How do we know how the action potential happens? What experiments have provided us with the evidence?

• What happens if the action potential is blocked in some way? How might that happen?

• Why are action potentials “all or nothing” events?

• How are EPSPs and IPSPs added up to determine whether an action potential will be generated in the post synaptic neuron?

Chapter 2

The Senses

All pathways from the sensory system pass through the thalamus EXCEPT for smell

Organ Brain region

Somatosenstation: pain, touch,

body awareness

Skin & Muscles SSC (parietal), cerebellum, basal ganglia

Olfaction: Smell

Nose (muscosa), olfactory bulb

Amygdala, pyriform region, orbiofrontal

cortex

Taste Mouth Somatosensory cortex, insula

Vision Eyes Occipital cortex

Audition: Hearing

Ears Temporal cortex

Chapter 3

Things to think about

• What is a receptive field?

• What do you think happens to the brain of an anopthalmic (somebody born without eyes)?

• What is synesthesia and how does it come about?

• Do the senses help each other out?

Chapter 3

Vision

- Light passes through the lens which focuses it on the fovea at the back of the eye

- The fovea has the greatest concentration of cones which are used for colour and fine detail vision

- Rods are used for light versus dark vision and are most active in darker conditions.

Chapter 4

- Cones send their input to P ganglion cells which travel to the 4 Parvocellular layers of the LGN

- Activity in the rods are collected by M ganglion cells which travel to the 2 Magnocellular layers of the LGN.

- Neurons travel from here to the primary visual cortex (V1) via the optic radiation

- From V1, activity passes to V2, V3, V4, V5 and the temporal and parietal cortices for more specialised processing.

- The two streams hypothesis (Goodale & Milner) posits that the stream passing to the temporal cortex is for object recognition, whilst the stream passing to the parietal cortex is for action and is thus called the What and How theory.

Chapter 4

Things to think about:

• Why do people need to wear glasses or contact lenses? How do they help?

• Why can we not see colours in very dim light conditions?

• Is there a difference in the visual problems people have with damage to either the parietal or temporal cortex.

Chapter 4

Hearing

- The pitch of a sound is created by the frequency of a sound wave and is measured in Hz

- The loudness of a sound is created by the amplitude of a sound wave as is measured in Db

- The outer ear (pinna) collects and amplifies sound waves. Sound waves that occur at about ~ 3,000 Hz (i.e. human speech) are selectively amplified.

- The middle ear (ear drum) transmits this sound energy mechanically to the fluid filled inner ear (cochlea).

- The inner ear (cochlea) converts these mechanical vibrations - into electrical signals via the basilar membrane which has a tonotopic map.

Chapter 5

- Action potentials are related to the brainstem then midbrain and onto the MGN in the thalamus before it get to the temporal lobe in the cortex.

- Language is usually processed in the left hemisphere with speech comprehension in the temporal lobe (Wernicke’s area) and production in the frontal lobe (Broca’s area).

- Music is processed in analogous regions of the right hemisphere.

- Reading and writing requires interaction between Wernicke’s and Broca’s area via the arcuate fasciculus.

Chapter 5

Things to think about:

• What is a tonotopic map? Is there something similar for vision?

• What do the differences between Broca’s and Wernicke’s aphasia tell us about how the brain processes and produces language.

See http://www.youtube.com/watch?v=aVhYN7NTIKU andhttp://www.youtube.com/watch?v=f2IiMEbMnPM

• How important is the tone of voice in speech comprehension?

Chapter 5

Movement

- Movements are planned in sequences of actions in the brain.

Brain region Function

Prefrontal cortex

Premotor cortex

Motor cortex

Spinal cord

Cerebellum

Basal ganglia

Makes the decision about what you want to do

Creates a plan of action to achieve what you want

Creates the actual action signals

Sends these signals to the muscles

Assesses movement accuracy

Determines movement force

Chapter 6

Things to think about:

• What happens to sensory experience and motor production if the right side of the spinal cord is severed?

• What is a homunclus?

• How can we explain motion sickness?

• Parkinson’s disease is characterised by jerky movements. How can this be explained by the pattern of damage seen in the substantia nigra in these patients?

• What might happen from damage to the cerebellum?See http://www.youtube.com/watch?v=5eBwn22Bnio

Chapter 6

Brain Development

- There are 6 main stages of brain development• Cell birth

• Cell migration

• Cell differentiation

• Cell growth and maturation

• Synaptic rearrangement and cell death

• Myelination

- Brain development happens throughout life. Some functions can be linked to myelination of the brain region involved, e.g. the pincer grip and myelination of the primary motor cortex.

Chapter 7

Things to think about:

• What advantages does genetic engineering have for medical science

• What developmental disorders can be linked to problems at each stage of brain development

• Do you believe in nature or nurture? Why?

• Why do young people sometimes make bad decisions?

Chapter 7

Behaviour

- Regulatory Behaviours are essential for survival:Homeostatic mechanisms keep certain body functions within a narrow fixed range. Examples are temperature control, eating and drinking, salt consumption, waste elimination etc.

- Non-regulatory behaviours are not essential for survival:- Examples include sexual behaviour, parenting, aggression, food preference, curiosity,

reading etc.

- Reward underlies all motivated behaviours.

- The hypothalamus is central to many behaviours as it is - involved in the balance of many hormones in the body.

Chapter 8

- Things to think about:

• Can anorexia and obesity be linked to a misbehaving brain? Explain.

• How do we know when to eat and when to stop eating?

• Why do we bother to do anything at all?

• What is the difference between an instinct and other behaviours?

Biorhythms

- Some biorhythms can be long as in circannual (hibernation for example) cycle or shorter such as circadian (sleep-wake) cycle.

- Our sleep-wake cycle is actually 26 hours long but light acts as a Zeitgerber (time giver) to constrain it to the 24 hours of the day.

- The SCN of the hypothalamus is integral to setting our sleep-wake cycle.

- Sleep is made up of a cycle of 4 non-REM stages and one REM stage.

- We are paralysed during REM sleep so sleep walking, talking and eating happens in non-REM sleep. These are termed parasomnias.

- Narcolepsy and cataplexy are disorders of REM sleep.

- REM sleep has a role in memory formation.

- The preoptic nucleus of the hypothalamus promotes sleep and the reticular activating system of the brainstem wakes us up.

Chapter 9

Things to think about:

• What would happen to our biorhythms if we lived in a bunker with no light at all?

• Why is it easier to deal with jet lag if you are flying from Europe to the USA as opposed to the other way round?

• How important are biorhythms in medicine?

• Why do you think we need to sleep?

• What results from damage to the reticular activating system?

Chapter 9

Sexual behaviour

- The genotype is the set of genes a person possesses. These genes are organised onto chromosomes.

- We have 23 pairs of chromosomes (23 from the mother and 23 from the father).

The 23rd pair consists of the sex chromosomes, XX in women and XY in men.

- The phenotype is the collection of observable traits of a person.

- The most important hormones in sexual and reproductive behaviour are androgens, oestrogens and progesterones. These are released in differing proportions by both male and female reproductive organs.

- We are a product of our genotype, the action of sex hormones pre-natally and the proportion of sex hormones post-natally.

Chapter 10

- The hypothalamus is involved in sexual behaviour whereas the amygdala is required for sexual motivation.

- The frontal lobe is also important in libido

- Dopamine creates the feeling of sexual reward and feeling of relaxation and bonding are generated by the release of oxytocin.

Chapter 10

Things to think about:

• Does the man or the woman determine the sex of their baby?

• How might it come about that the phenotype does not correlate with the genotype?

• Do the biological differences between men and women lead to cognitive differences?

• How are pheromones important in behaviour?

Chapter 10

Emotion

- Emotional stimuli are relayed by the sensory systems to the amygdala.

- The perception of emotion is created by a direct signal to the frontal cortex and an indirect signal through the hypothalamus.

- The hypothalamus changes our bodily affect by action on the autonomic nervous system which increases heart rate, causes a dry mouth etc.

- The amygdala is vitally important in the processing of fear and is also important in emotional learning involving fear (emotional conditioning).

- The cerebral cortex is important in interpreting the emotional signals coming from the autonomic nervous system from the hypothalamus and the amygdala.

- .

Chapter 11

- Affective mood disorders (e.g. depression) appears to be related to communication between the amygdala and frontal cortex. The neurotransmitter serotonin is often depleted in these cases.

- The right hemisphere is especially important in the expression and comprehension of emotional aspects of speech (intonation).

- The left hemisphere is associated with positive emotions, whereas the right hemisphere is more involved with negative ones

Chapter 11

Things to think about:

• What might happen to the perception of emotion in cases of spinal cord injury?

• Why do children have tantrums?

• How do selective serotonin reuptake inhibitors act in the case of depression?

• You have a patient who has a large lesion to the left frontal lobe. What effect on their emotions would you expect?

• Is it possible to control your emotions? How might you go about doing that?

Chapter 11

Learning and Memory

- Learning is a relatively permanent change in an organism’s behaviour as a result of experience.

- Memory is the ability to recall previous experiences.

- Memory can also be short term (including working memory) or long term.

Chapter 12

- Procedural learning involves cerebellum circuits and such memories are stored in the basal ganglia and premotor regions.

Chapter 12

- Declarative memories require activity in the hippocampus which is also important in spatial learning and memory (particularly important in animals like birds who cache food and London Taxi Drivers).

- The amygdala is important in emotional memory.

- Autobiographical memory is a form of episodic memory for things that happened to you. The frontal cortex is important for such memories.

- “Cells that fire together, wire together.”

Things to think about:

• How accurate is memory? How might its constructive nature increase its fallibility?

• What is PTSD and how does it arise?

• What kinds of brain damage leads to different forms of amnesia?

• What effect does alcohol and alcoholism have on memory?

• Does age affect memory function? How does it affect our ability to learn?

Chapter 12

Thinking and consciousness

- Much research relating to consciousness seeks to measure the sub-conscious.

- Blindsight occurs from damage to the occipital cortex. Patients are unable to consciously see stimuli but they are aware of their presence. Therefore, activity of the occipital cortex is necessary for conscious vision.

- Neglect is caused by damage to the parietal cortex. Patients can’t orient their attention to the contra-lesional side of space. However, they can sub-consciously take information on this side into account.

- Damage to the ventral stream means patients cannot identify objects. But when asked to use the object, they do so correctly.

- Language is important in consciousness as split brain patients cannot “see” objects presented to their left side. The information arriving in the right hemisphere can not pass to the left hemisphere to be verbalised.

- Consciousness may be linked to synchronised firing rates between neurons of different regions.

Chapter 13

Things to think about:

• What is “Theory of mind” and how is it manifested in the brain?

• Is there a consciousness region?

• What are the stages of unconsciousness?

• Do we all experience the world the same way or is there a difference between our subjective consciousnesses? Why might that be?

• If you were an alien visiting Earth for the first time, what would you think are the main advantages and disadvantages of the human brain?

• Is there a reality outside of our consciousness or does our consciousness determine reality?

Chapter 13

Medical science and medical practice

- Thalamocortical dysrhytmia underlies many neurobehavoural disorders such as Parkinson’s disease, tinnitus, migraine, dystonia etc.

- It is characterised by a nucleus specific to a particular function in the thalamus sending out a sleep rhythm to a particular part of the cortex.

- It can be mediated by the insertion of a pacemaker in the brain to regulate these signals (deep brain stimulation).

- Stem cells can be used to regrow tissue specific to the region in which they are inserted.

- Such treatments have had varying success in Huntington’s Disease and Parkinson’s disease as well as spinal injuries.

- Neurostimulation can be used to improve the brain’s receptivity to neurorehabilitation following stroke

Chapter 14

Things to think about:

• Do you think there is an appreciable gap between medical science and medical practice? What steps could be taken to change this?

• Is it ethical to test treatment on dying patients who are willing?

Chapter 14