Lecture III

Question 1

Single-unit recording (SUR)

Answer 1

Recording electrophysiological activity (APs) from a single neuron.
Very high spatial resolution.
High temporal resolution.

Question 2

Differences of SUR with EEG (2):

Answer 2

SUR more localized - better spatial resolution.

SUR measures APs - EEG measures EPSPs/IPSPs.

Question 3

To study SUR (4 steps):

Answer 3

Record raw electrical fields inside the brain.
Then filter the signal.
Then start identifying different units/neurons.
Analyze events.

Question 4

Low-pass filter

Answer 4

Filters out LFPs coming from surrounding neurons to use - only LFPs from surrounding.

Question 5

High-pass filter

Answer 5

Filters out APs coming from target neurons to use.

Question 6

Low-pass filter and frequencies

Answer 6

Low-pass filter - only low frequencies can pass - surrounding neurons have low frequency because LFP not AP.

Center/target neurons have high frequencies because AP not LFP so require high-pass filter.

Question 7

SUR - pathway AP generation.

Answer 7

RMP - K+ channels are open, Na+ channels are closed.
Depolarization to threshold - K+ and Na+ closed.
Depolarization to AP - K+ efflux, Na+ influx.
Hyperpolarization to beneath RMP - K+ efflux, Na+ inactive.
Small depolarization to RMP - K+ open both ways, Na+ closed.

Question 8

mV of RMP, threshold, peak AP

Answer 8

RMP = -65 mV
Threshold = -40 mV
AP = up to +30 mV

Question 9

APs may look different because …, but since APs are always the same, this …

Answer 9

Because they come from different angles, this helps identifying the different neurons.

Question 10

Peristimulus time histogram (PSTH) shows…

Answer 10

The spike counts over many trials.

Question 11

Purpose of multi-unit recording (MUR) (3):

Answer 11

Reduce number of experimental animals.
Parallel recording tells the functioning of a system.
More and better data.

Question 12

Outer ear -
Middle ear -
Inner ear -

Answer 12

Outer ear - amplifies sound at frequency wave important for speech perception, helps front to back localization.

Middle ear - filled with fluid and also acts as amplifier, transduces air pressure waves into fluid waves.

Inner ear - transduces fluid waves into neural activity, maintaining balance.

Question 13

Power density of sound -

Cochleogram -

Answer 13

Power density of sound - use as function of time and frequency.
Cochleogram - use as function of time and place.

Question 14

Pathway sound waves to brain.

Answer 14

Changes in air pressure are transmitted to changes in fluid pressure in inner ear.
Changes induce movement of basilar membrane and stereocilia of hair cells.
Movements are turned into electrical signals.
Mechanoreceptors open and permit K+ influx into hair cell.
Causing depolarization due to differences of K+ in endolymph and perilymph.
Changes in MP lead to APs and NT release - Ca2+ influx.
NTs bind to auditory nerve to brain.

Question 15

Frequency mapping:

Answer 15

Low frequencies at apex.

High frequencies at base.

Question 16

Pathway cochlea to auditory cortex.

Answer 16

Cochlea - cochlear nucleus - superior olivary nucleus (SON in medulla) - partly cross-over - inferior colliculus - medial geniculate nucleus of thalamus - auditory cortex in temporal lobe.

Question 17

Location primary and secondary auditory cortex.

Answer 17

Primary superior on superior temporal gyrus, secondary inferior on superior temporal gyrus.

Question 18

Superior olivary complex (2):

Answer 18

First interaction between information from both ears, e.g. localization.
Brainstem nuclei - extends from medulla to pons.

Question 19

Medial superior olive/MSO

Answer 19

Sound localization by interaural time differences, < 3000 Hz.

Question 20

Lateral superior olive/LSO

Answer 20

Sound localization by interaural intensity differences, > 3000 Hz.

Question 21

MSO and LSO

Answer 21

Neuronal map where neurons respond most strongly when APs from two ears arrive simultaneously.

Ipsilateral excitation and simultaneously contralateral inhibition.

Question 22

Inferior colliculus … cues for sound localization in space and contains …

Answer 22

Integrates cues and contains topographical representation of audible space.

Question 23

Inferior colliculus (4):

Answer 23

Major integration center.
Interaction with motor system to guide behavior.
Has complete map of auditory space.
Lies in the superior caudal midbrain.

Question 24

Medial geniculate nucleus of thalamus (2):

Answer 24

Key relay station of information to divide in cortex.

Influences direction and maintenance of attention.

Question 25

Where takes higher-order processing place?

Answer 25

In belt areas, including speech, word recognition and comprehension.

Question 26

Pitch is the … of … and … tones.

Answer 26

Ordered perception of high and low tones.

Question 27

… and … are processed differently in the auditory cortex.

Answer 27

Pitch and frequency

Question 28

Most information crosses over, however hemispheres process stimuli from both ipsilateral and contralateral sides. 2 advantages:

Answer 28

One sided brain damage causes little impact.

More processing potential.

Question 29

Pathway cochlea - auditory cortex.

Answer 29

Cochlear nucleus - superior olivary complex - inferior colliculus - medial geniculate nucleus of thalamus - auditory cortex.

Question 30

Auditory cortex is arranged tonotopically by frequency.

Answer 30

Apex - low frequencies > 25 Hz

Base - high frequencies > 1600 Hz

Question 31

3 small bones in middle ear:

Answer 31

Malleus, incus, stapes.

Question 32

Higher pitches are the result of … frequencies of sound waves.
Lower pitches are the result of … frequencies of sound waves.

Answer 32

Higher

Lower

Question 33

Depending on frequency, it’s going to cause a different section of the basilar membrane to vibrate.
Easier to move … membrane than … membrane
… is … than …
… frequencies (…) need more force to vibrate.

Answer 33

Easier to move thinner than thicker membrane.
Apex is thicker than base.
Low frequencies (apex) need more force to vibrate - therefore more difficult to hear.

Question 34

Endolymph - … K+, … mV, like…, … Na+, scala …

Perilymph - … K+, … mV, like…, … Na+, scala …

Answer 34

Endolymph - high K+, + 80 mV, like intracellular fluid, low Na+, scala media.
Perilymph - low K+, 0 mV, like exracellular fluid, high Na+, scala tympani.