Psych Week 20 (Bio) - Sleep, Audition and Investigating the Brain

What is structural imaging of the brain?

• CT scan - contrast dye injected into blood, X rays sent out at different angles and scanner rotates to take measurements at each angle

• MRI scan - powerful magnetic field applied and atoms in brain release electromagnetic energy which is measured

What is activity imaging of the brain?

• EEG (example of electrophysiology) - scalp signal, sensitive to postsynaptic dendritic currents

What are the five types of brain wave (measured by EEG) emitted by the nervous system and what do they mean?

• Delta (0.5-4 Hz) → sleep

• Theta (4-7 Hz) → light sleep, meditation

• Alpha (8-12 Hz) → relaxation, unfocused

• Beta (12-30 Hz) → alertness, attention, REM sleep

• Gamma (30-100 Hz) → highly alert and conscious

How can the effects of brain damage be observed?

• Watching patient

• e.g. Phineas Gage had rod through head, had intact speech and movement but disinhibition of inappropriate behaviour and changed personality

• Gage had damage to prefrontal cortex

How can trials be used to assess the effects of brain damage?

• Patient with limbic system dysfunction in the amygdala asked to draw different emotional states

• Amygdala dysfunction caused difficulty in drawing fear and anxiety

What are three methods for neuropsychological animal studies?

• Single-cell recordings using microelectrodes (records, does not stimulate)

• Electrical brain stimulation

• Lesion studies (brain damaged on purpose and cognitive effects are observed)

What is TMS as a modern brain stimulation method?

• Transcranial magnetic stimulation

• Non-invasive

• Neurons stimulated by electromagnetic coil above head

What is ERP as a modern brain stimulation method?

• Event-related potentials

• EEG activity, but time-locked to an external event (e.g. sound)

What is functional imaging of the brain?

• fMRI - detects increase in oxygen levels with a haemodynamic response function (i.e. Hb has magnetic properties)

• PET - measures local blood flow into a brain region by injecting a radioactive tracer into the blood stream

What are circannual and circadian rhythms?

• Circannual ~ a year

• Circadian ~ a day

• Endogenously generated

• Can be modulated by external cues like sunlight or temperature

What are the mechanisms of the human biological clock?

• Suprachiasmatic nucleus in the hypothalamus is centre for circadian rhythms of sleep and temperature

• Light influences clock

What are the four stages of the sleep cycle?

• Stage 1 - light sleep, short, reduced muscle activity

• Stage 2 - sleep spindles and K-complexes seen on polysomnograph

• Stage 3 - slow-wave sleep, deep sleep, brain activity decreases, heart rate and temp. decrease

• REM - partial paralysis, dreaming, increased brain activity, heart rate and blood pressure

What are examples of sleep disorders?

• Deprivation (affects things like metabolism)

• Irregularity (causes poor cognitive function)

• Insomnia (shifts in circadian rhythm)

• Sleep apnea (inability to breathe in sleep)

• Narcolepsy (unexpected sleepiness in day)

What are the functions of sleep?

• Conserves energy

• Animals sleep more during food shortages

• Critical for memory consolidation

• Some animals have unihemispheric slow-wave sleep (one side of brain is asleep, other is awake) to allow breathing at ocean surface (e.g. dolphin)

Which part of the brain is responsible for hearing?

• Auditory cortex in the temporal lobe

• Cortex has tonotopic organisation - the more anterior the firing neuron, the lower the pitch

What is the structure of the human ear?

• Outer ear - pinna

  • Captures and amplifies sound

• Middle ear

  • Eardrum collects vibrations and transmits to ossicles, where lever action transfers to cochlea

• Inner ear

  • Cochlea div idea into 3 fluid-filled canals (vestibular, tympanic, cochlear)

  • Vibrations sent to organ of Corti

What is intensity as a sound property?

• How much air fluctuation the sound creates

• Volume is a perceptual correlate of intensity

• Measured in dB on a logarithmic scale

• Encoded by neuron firing rate - higher the rate, the louder the sound

What is frequency as a sound property?

• Number of compression/rarefaction cycles per second

• Pitch is a perceptual correlate of frequency

What are the three main binaural cues for sound localisation?

• Different intensities between two ears

• Different time of arrival between two ears

• Phase difference between two ears

What is lateralised processing?

• Processing of information is divided into left and right sides of the body e.g. right ear dominance for speed recognition as has more connections to left hemisphere

• Sex can influence laterality

• Right or left-handedness can influence laterality

What is conductive hearing loss?

• Results from damage to the eardrum or ossicles in the middle ear, so a failure to transmit intact sound to the cochlea

• Bone conduction issues

What is sensorineural hearing loss?

• Damage to part of the cochlea or hair cells in the inner ear

• Congenital, a result of a disease or repeated exposure to loud noises

What is tinnitus?

• ‘Ringing’

• Sound perception within the human ear in the absence of corresponding external sound