Global brain activity + Association cortices

Question 1

The Electroencephalogram

Answer 1

• measures the change of the voltage of dendrites in pyramidal cells in the cerebral cortex
• there are standard placements for the EEG
  
  • Occipital, Parietal, Frontal, Temporal, Auricle, Central
  • pairs of electrodes measure the difference in voltage between two points: measures the slightly negative extracellular fluid caused by depolarization of many millions of axons
• the more synchronized the firing of the pyramidal cells the greater the amplitude recorded by the EEG (also the number of cells also contributes to this)
• the population of neurons must be aligned in a parallel orientation so that they summat rather than cancel out

Question 2

What layers does the EEG need to travel through?

Answer 2

• Scalp
• Scull
• Dura Mater
• Arachnoid
• Subarachnoid space
• Pia Mater

Question 3

Explain thalamic neurons generate synchronous rhythms

Answer 3

• have specific voltage-gated ion channels that produce a rhythmic self-sustaining AP discharge
• synaptic connections between excitatory and inhibitory thalamic neurons force each individual neuron to conform
• this is then transferred to the cortex via thalamocortical axons, which excite a large number of cortisol axons

Question 4

What are the behavioural criteria for sleep?

Answer 4

• Reduced motor activity
• Decreased response to stimulation
• Stereotypic postures
• Relatively easy reversibility

Question 5

What are the characteristics of the three functional states of Sleep

Answer 5

• Awake
  
  • low voltage, fast EEG
  • often have Rapid eye movement
  • movement is continuous and voluntary
  • thought is logical progressive, and sensations are vivid and externally generated
• Non-REM
  
  • high voltage, slow EEG
  • rarely have REM
  • movement is occasional, involuntary
  • thought is logical, repetitive, the sensation is dull or absent
• REM
  
  • low voltage, fast EEG
  • often REM
  • movement: muscle paralysis, commands from the brain ignored
  • thought is vivid, illogical bizarre, sensations are vivid and internally generated

Question 6

Functions of Sleep and Dreaming

Answer 6

• conservation of metabolic energy
• Cognition
• Thermoregulation
• Neural maturation and mental health

Question 7

Imaging techniques for the brain

Answer 7

• Structural imaging: Measures of the spatial configuration of types of tissue in the brain (static maps)
  
  • Computerised Tomography, CT
  • Magnetic resonance imaging, MRI
• Functional imaging: Measures the moment-to-moment variable characteristics of the brain that may be associated with changes in cognitive processing (dynamic maps): usually compared against experimental baseline conditions
  
  • Positron Emission Tomography, PET
    
    • measures change of blood flow to certain regions of the brain (based on neuronal activity)
  • Functional magnetic resonance imaging, fMRI
    
    • sensitive to conc. of oxygen in the blood

Question 8

The use of CT scans in the brain

Answer 8

• Based on the amount of X-ray absorption in different types of tissue.
  
  • Bone absorbs the most (the skull appears white),
  • Cerebrospinal fluid absorbs the least (the ventricles appear black)
  • the brain matter is intermediate (grey).
• Used in clinical settings, e.g. to diagnose tumours or identify haemorrhaging or other gross brain anomalies.

Question 9

The use of MRI scans in the brain

Answer 9

Provides a much better spatial resolution.

• Provides better discrimination between white and grey matter.
• Can be adapted for detecting the changes in blood oxygenation associated with neural activity (fMRI).
• external magnetic field, briefly orients the magnetic fields of the protons so they are perpendicular: this produces a measurable MR signal

Question 10

The use of PET scanning in the brain

Answer 10

• Based on blood volume
• Involves radioactivity (signal depends on radioactive tracer)
• Participants scanned once or few times
  
  • Temporal resolution: 30”
  • Effective spatial resolution: 10mm
• Sensitive to the whole brain
• Can use pharmacological tracers

Question 11

The use of (BOLD) fMRI in the brain

Answer 11

BOLD signal: blood-oxygen-level-dependent contrast, is the signal measured in fMRI that relates to the concentration of oxy- and deoxyhaemoglobin in the blood.

• Based on blood oxygen concentration
• No radioactivity (signal depends on deoxyhaemoglobin levels)
• Participants scanned many times
  
  • Temporal resolution: 1-4”
  • Spatial resolution: 1mm
• Some brain regions (e.g. near sinuses) are hard to image

Question 12

Give an overview of Hierarchical organization of sensory systems

Answer 12

(going from higher to lower levels- the higher systems build up and receive inputs from lower systems )

• Association cortex
  
  • ​Unimodal association areas
  • Multimodal association areas
• Secondary sensory cortex
  
  • ​Multimodal sensory association areas project to multimodal motor association areas (rostral to M1)
• Primary sensory cortex
  
  • ​the primary sensory area is the initial stage of processing whilst the primary motor area is the final stage of processing
• Thalamic relay nuclei
• Receptors

Question 13

Give an overview of the three main Multimodal Association areas

Answer 13

• Posterior association area (perception, language)
• Temporal association area (emotion, memory)
• Prefrontal association area (executive functions)
  
  • a convergence of 5 corticocortical pathways are seen in monkeys

Question 14

What is Agnosia?

Answer 14

• this is a disorder of high-level sensory analysis
  
  • caused by damage to the temporal lobe
• when an individual is able to identify or recognize an object, person or sound using one or more of their senses despite having normally functioning senses
• Prosopagnosia: the inability to recognize and identify faces
• Apperceptive agnosia: failure to recognize due to deficits in the early stages of perceptual processing
• Associative agnosia: failure of recognition despite there being no deficit in perception
• Associative agnosia patients can typically draw, match or copy objects while apperceptive agnosia patients cannot

Question 15

What are the Executive Functions of the Prefrontal cortex?

Answer 15

• executive function is when you have to concentrate and pay attention when automatic or relying on instinct/ intuition is not the best course of action
• Inhibition control:
  
  • ​including self-control and behavioural inhibition
  • Interference control: selective attention and cognitive inhibition
• Working Memory
• Cognitive flexibility:
  
  • ​set-shifting, mental flexibility - closely linked with creativity

Question 16

Explain the sequence of information processing in the motor system

Answer 16

• motor planning is revers to sensory information processing
• a general outline of behaviour –> concrete motor response
• Frontal cortex: individual neurons fire for a range of related behaviours (not specific motor responses).
• Movements and complex actions result from patterns of firing of large networks of neurons in the frontal lobe.
• The premotor cortex generates motors programs and the neurons are active during the preparation of movement.
• Motor cortex neurons mainly fire to produce movements in particular directions around specific joints.

Question 17

What are the specialised language areas in the brain and what are their roles in language?

Answer 17

• Broca’s area which is just above the gyrus anterior to the motor cortex
• Wernicke’s area
• Language comes into the brain through visual and auditory systems
• Motor system: Produces speech, writing
• Processing between sensory and motor systems; Essence of language

Question 18

What is Aphasia?

Answer 18

• partial or complete loss of language abilities following brain damage, often without the loss of cognitive faculties or the ability to move the muscles used in speech. can also apply to sign language
• lesions in left frontal lobe in the Broca’s region affect the ability to produce language efficiently
  
  • motor/expressive aphasia or Broca’s aphasia
• lesions in the left posterior temporal lobe in Wernicke’s area cause difficulty understanding language.
  
  • sensory/ receptive aphasia or Wernicke’s aphasia
• Conduction aphasia: the inability to produce appropriate responses to heard and understood communication
  
  • due to disorders/ lesions in the pathways connecting the relevant frontal and temporal language pathways (Broca’s- Wernicke’s areas)

Question 19

Give an overview of split-brain studies and Asymmetrical language processing

Answer 19

• If a split-brain person sees a word in the left visual field, he will say he sees nothing.
• This is because the left hemisphere, which usually controls speech, did not see the word, and the right hemisphere, which saw the word, cannot speak.
• However, the left hand, which is controlled by the right hemisphere, can pick out the object corresponding to the word by touch alone.