Sakata Lectures Flashcards
1
Q
What are the two brain systems that local navigation uses?
A
- Uses multiple parallel brain systems.
(1) [Dorsolateral] Striatal System
- Habitual ‘stimulus-response’ (motor-based system)
(2) Hippocampal system - Flexible _ using external associations.
- Squirrels rely on tits memory (flexibly navigate and rely on memory cues, rather than scent cues, to retrieve hidden nuts).
(hippocampal-lesioned rats show no preference to the correct quadrant)
2
Q
Different cues for different scales
A
(1) Long-distance phase
- celestial cues, magnetic fields
(2) Homing phase
- odour gradients, soundscapes
(3) Pinpointing-the-goal-phase
- specific odours, landmarks
3
Q
The Brain’s Internal GPS
A
- many types of neurons are involved in spatial navigation and mapping.
- place cells
- grid cells
- head direction cells
- border cells
-speed cells
4
Q
The Hippocampal Trisynaptic Circuit
A
Composed of 3 major subregions
1) Dendate gyrus (granule cells)
- major input into the hippocampal circuit receiving information from the enterohinal cortex.
2) CA3 (pyramidal cells)
3) CA1 (pyramidal cells)
There are association areas with combined sensory inputs. they project to the parahippocampal cortex (where pathway) and parirhinal cortex (what pathway).
These then project tot he enterohinal cortex that project to the hippocampus.
first to dentate gyrus then CA3 then CA1 then Subiculum then back to the enterohinal cortex.
5
Q
How could many place cells work together to help an animal navigate its environment?
A
- hippocampal place cells fire at distinct spatial locations.
-the ‘tiling’ of these cells across an environment can create a ‘map’ of space in the hippocampus. - the ‘cognitive map’ helps the animals navigate itself in relation other cues in space and plan out trajectories towards goals.
- multiple place cells map an environment.
6
Q
Is there a topographic relationship between place fields of neighboring cells?
A
No
7
Q
Are place cells exclusive to mammals?
A
- No; spatially tuned cells exist in food-catching birds.
- Cells are more spatially tuned towards the anterior portion of avian hippocampus (shows spatial tuning).
- In humans, it is posterior regions. (spatial memory and navigation).
- In rodents, spatially tuned cells are more common in the dorsal hippocampus.
8
Q
What is spatial tuning in the hippocampus like for birds?
A
- it depends on ethological needs.
- in ‘non-catching food birds’ there are fewer and less spatial tuned cells than in food-catching birds.
- most-studies on place cells are carried out in small boxes or linear tracks (mazes with walls & stuff)
- the disadvantage is that it does not represent complex environment in wild, might not show natural behaviour.
- in a large space, a single place cell can fire at multiple distinct locations, showing hippocampus ability to encode multiple locations within a large spatial context.
- there are cool studies with bats, in a large space (200m tunnel monitored with wireless electrophysiology system), insight into how place cells work in a vast environment, multiple place fields per cell, variable field sizes.
- animals that navigate larger spaces have larger place fields in addition to small place fields, shared by same place cells.
9
Q
What are some key takeaways from ‘Navigation’?
A
- animals use a variety of navigational strategies, both within and across scales.
- flexible navigation requires the use of the hippocampus.
- animals use an internal spatial map to flexibly navigate their local surroundings.
- this spatial or ‘cognitive map’ is made from place cells in the hippocampus, with each cell tuned to a specific place in the environment.
- unlike most sensory systems, place cells do not showcase any topographic organization in the hippocampus with respect to space but do tend to be more spatially tuned towards the anterior end in bird (dorsal in mammals).
- animals that navigate larger spaces likely have larger place fields in addition to smaller place fields, shared by the same place cells.
10
Q
What do we know about echolocation and blind people?
A
- echolocation is not uncommon in blind people.
- echolocation in humans has only recently been studied by scientist.
-clicks with echoes activates visual, not auditory brain regions compared to click without echoes in blind but not sighted people.
11
Q
What is sensorimotor integration?
A
Sensorimotor integration refers to the process by which the brain uses sensory information to shape motor output. This sensory information could stem from sources outside the individual or self-generated sensory stimuli.
12
Q
Discuss sensorimotor integration in owls.
A
- how owls localize prey based on sounds produced by prey.
- sensory information sent to tegmentum and transformed into a motor command for head movement.
- stimulating different parts of the optic tectum leads owls to turn their heads in different directions.
- direction and magnitude of tuning depends on the receptive fields of neurons that are stimulated.
13
Q
How do bats use echolocation as a form of sensorimotor integration?
A
- bats use self-generated sounds and echoes from these sounds to gather information about their environment and influence their behaviour.
- active sensing: animal interacts with environment with self-generated energy (as opposed to passive sensing)
14
Q
How does the echolocation (vocal) behaviour of the bat change as it pursues a prey?
A
- Marco Polo
- Bats change their rate of calling during hunting
(1) Approach (10Hz)
(2) Track (60Hz)
(3) Terminal (200Hz)
15
Q
What spatial information does a bat need to gather about its prey?
A
- location along the azimuth.
- location along the elevation axis.
- distance.
- relative velocity.
- direction of movement.
- other things (e.g., size)
These types of information can be learned from comparing the call that the bat produces to the sound of the echo (e.g., the delay between pulse emission and the echo serves as a proxy for the distance of the prey)
16
Q
Why are the calls that bats use for hunting (a) so high in frequency (pitch) and (b) so high in amplitude?
A
(1)
calls need to be high in frequency (ultrasonic) because the wavelengths need to be shorter (smaller) than the prey (insects) in order for an echo to be generated (for sound to bounce off an object).
(2)
calls need to be loud because the amplitude attenuates very quickly due to spherical spreading and atmospheric attenuation (particle collisions). In addition, the call needs to travel to the object, the echo needs to come back to the bat, thereby increase the distance the sound travel (therefore, experiment more attenuation)
Higher frequencies attenuate more rapidly than lower frequencies, so the ultrasonic needs to be even louder.
17
Q
CF-FM bats have auditory fovea, whereas FM bats do not. Where is the auditory fovea and why do FM bats not have it?
A
- auditory fovea is in the cochlea.
- the calls of the FM bats are not concentrated around one frequency, but have a broad range of frequencies.
- there is no one frequency that should be overrepresented in their auditory system.
18
Q
Spherical spreading loss
A
- attenuation of sound with distance limits range of echolocation.
- sound intensity drops with square distance.
- the amplitude of a sound drops quickly as the sound travels away from the sound source because of the spreading of the signal as it moves through the environment.
19
Q
Atmospheric attenuation (absorption)
A
- sound amplitude decreases due to particle collisions.
- the rate decrease in amplitude with distance varies with the frequency of sound. The amplitude drops with scare frequency (more atmospheric attenuation for higher frequency of sound)
- this means that the ultrasonic pulses generated by bats attenuate rapidly in the environment.
20
Q
Why are bat calls so loud?
A
- Bats need to produce high frequency sounds to detect echoes from small insects.
- High frequency sounds attenuate much faster than lower frequency sounds.
- Bats are processing the echoes off objects, and sounds undergo both types of attenuation (spherical spreading and atmospheric attenuation) on the way out AND on the way back (echoes).
- Both types of attenuation (spherical spreading and atmospheric attenuation) on the way out AND the way back (echoes)
21
Q
How do bats use echoes to gather information about location of objects? (azimuth, elevation, distance, direction, and speed of movement)?
A
- azimuth and elevation assessed using ITD and IID (as well as by moving ears).
- distance inferred from the time delays between emitted sound and retuning echo. (pulses must be short to minimize temporal overlap between emitted sound and echo). the longer the delay between the call generated by the bat and the echo, the farther the object is away from the bat.
- direction and speed of movement inferred by Doppler shift.
22
Q
What are the types of bat calls?
A
1) frequency-modulated (FM) calls
- one of the benefits of FM calls for echolocation is that the delay of echo (relative to the call itself) can be compared across multiple frequencies.
2) constant-frequency & frequency-modulated (CM-FM) calls.
23
Q
Fundamental frequency and harmonics
A
- when a vibrating sound source like the larynx (or guitar string) generates a sound, it generates not only the fundamental frequency but also multiples of the fundamental frequency (e.g., the 2nd harmonic is twice the frequency of the 1st harmonic)
- when bats generate the sound, not only do they produce the fundamental frequency, but also the harmonics.
24
Q
What happens during the terminal buzz?
A
- cells are produced a rapid rate (e.g., 200 Hz).
- Bats shortened these calls, and these calls have a more rapid modulation of frequency over time (steeper slope).
- shortening of calls reduced pulse-echo overlap.
- narrower bandwidth and slightly lower in frequency during final buzz.
25
During CF-FM call, what are characteristics of the capture period?
- increased call rate right before capture
- calls are shorter and more steeply frequency modulated
- greater proportion of the CF-FM calls is FM (CF portion shortens)
26
Why do bats have distinct calls?
- Different call types produced by bats with different hunting strategies.
- Bats that hunt in dense forests or in vegetation close to the ground typically have calls with a strong FM component (or only a FM component)
- Bats that hunt in more open environments tend to emit calls with longer CF components.
27
What different information do FM vs CF-FM calls extract?
o FM calls are particularly good for determining target distance because distance (delays) can be calculated across multiple frequencies.
o CF portion of calls are particularly good for detecting objects in the environment because sound energy is concentrated at a specific frequency (not distributed across multiple frequencies); therefore, sound can travel farther with echoes more likely to be heard.
o Species that produce CF-FM calls have auditory systems tuned to narrower range of frequencies [so more sensitive to (i.e.., specialized for) echoes]
o CF portion of calls better for extracting the speed and direction of a prey item (can use Doppler shift)
28
How does the nervous system encode the delay between a pulse and an echo?
- Jeffress model
- Proposes that axon lengths act as delay lines and that neurons that detect the coincidence of inputs (i.e., coincidence detectors) are important for the processing of ITDs.
- the distance of a prey could be computer using delay-tuning
neurons. These are neurons tuned to specific range of echo-delays [the time between a bat call (pulse) and its echo]
- when pulse is generated, information goes down. when echo is generated, the information countercurrent flow, meet at coincidence detector and then high firing rate of a particular cell.
29
How might these delay-neurons affect the vocal behaviour of hunting bats?
- the call rate changes as the bat approaches a prey.
- neurons that encode shorter delays might be connected to circuits that increase the rate of call generation.
30
Doppler Shift (DS)
- The Doppler shift described the change in the frequency of a wave as a source moves closer or farther away from a listener.
- How the frequency changes (moves up or down) and the magnitude of change depends on the relative direction and speed of the sound source.
- Occurs when either the sound source or receiver is moving.
(1) Stationary Source:
- Receivers experience the same frequency emitted by the stationary source, equidistant from it on both sides.
(2) Moving Source:
- The receiver on the right experiences a higher frequency (shorter wavelengths) as the source approaches.
The receiver on the left experiences a lower frequency (longer wavelengths) as the source moves away.
31
What does a doppler shift "look" like?
- sound is higher in frequency as the speaker approaches the microphone
- sound is lower in frequency as the speaker moves away from the microphone
- the multiple bright bands in the spectrogram are the harmonics of the fundamental frequency of the sound.
- the fundamental frequency and the harmonics at this point (where the microphone is) represent the true acoustic features of the sound being played back from the speaker.
- the greater the speed of the moving sound source, the greater the doppler shift (up and down depending on the direction).
- in the case of echolocation, the bat is the "source" (call) and "receiver" (echo).
- this means that the bat has information about the frequency of the sound it produces as well as the frequency of the echo. Therefore, it can compare the difference between the frequency of the call it produces and the frequency of the echo it hears.
- echo is higher in frequency than the pulse due to doppler shift.
- delayed echo can come back at different frequency than call (cause of doppler shift)
32
When the bat is moving closer to the prey, will the echo be higher in frequency than the call? What about when the bat is moving away?
1) Bat is moving closer to the prey, so the echo will be higher in frequency than the call.
2) Bat is moving away from the prey, so the echo will be lower in frequency than the call.
3) Moth is moving closer to the stationary bat, so the echo will be higher in frequency than the call.
4) Moth is moving away from the stationary bat, so the echo will be lower in frequency than the call.
33
Characteristics of CF-FM bats auditory system
- auditory system of CF-FM bats is sharply tuned to the species call frequency.
- the auditory system of CF-FM bats (horse bat and mustaches bat) is highly sensitive to narrow range of frequencies (vs. FM bats)
- auditory system of FM bats is more broadly tuned to frequency.
34
Individual Differences in CF Frequencies and Cochlear Specialization in CF-FM Bats
Figure Summary: The plot shows the amplitude of sound at different frequencies needed to activate neurons in the cochlear nucleus (hindbrain) of a mustache bat.
Key Observations:
Neurons are most sensitive to the frequency where the plot line occurs, meaning the lowest sound amplitude is needed for activation.
Cochlear specializations contribute to this tuning.
The basilar membrane has a large portion tuned to the species’ typical frequency.
The plot shows the frequency that causes maximal displacement of the basilar membrane, which follows a highly non-linear curve:
At the base (~0% distance), maximal displacement occurs at around 110 kHz.
As you move toward the apex, lower frequencies are encoded.
At 63 kHz, the basilar membrane is maximally displaced.
A large portion of the basilar membrane is tuned to the individual’s CF frequency.
35
Tonotopic organization of cochlea
- high-frequency sound activates hair cells towards the base of the cochlea.
- low-frequency sound activates hair cells towards the apex of the cochlea.
36
Interpreting Doppler shift (+) vs (-)
(+) shift:
- distance is decreasing (bat closing in on prey)
- echo frequency > than pulse
- the faster the bat approaches, the longer the upward shift.
(-) shift:
- distance is increasing (prey moving away or bat flying away)
- echo frequency is lower than the pulse.
- the fast the seperation, the larger the downward shift.
37
Explain "the auditory system of CF-FM bats is sharply tuned to the species call frequency"
- for example, the auditory system of CF-FM bats is highly tuned to a narrow range of frequencies. Whereas a FM bat, auditory system is broadly tuned to frequency.
- there are individual differences (within species) in CF-frequencies, and the auditory system of CF-FM bats is sharply tuned to the individuals call frequency.
- tuning in the auditory system: the cochlear nucleus ( in the hindbrain) contains neurons that are finely tuned to a specific sound frequencies) can see that neurons are most sensitive to the bats CF frequency (lowest amplitude required to activate them)
- the basilar membrane in the bats cochlea plays a key role in frequency discrimination.
- base of the membrane - tuned to high frequency.
- apex of membrane - tuned to low frequency.
38
A larger portion of the basilar membrane is tuned to species-typical CF frequency. Give an example.
- In mustache bats, a specific area of the basilar membrane is tuned to 63 kHz. this allows the bats to focus on echoes matching its CF call for better discrimination of prey or objects.
- auditory fovea: disproportionally large part of cochlea dedicated to frequencies around individuals CF.
- when looking at the tonotopic organization in part of the auditory cortex of mustached bat, see over-representation of individuals & species typical CFs in parts of the auditory cortex of CF-FM bats. get non-lineat auditory sound in autidory cortex (massive expansion).
39
In the mustache bat, there is a disproportionally large representation of sharply tuned neurons in the frequency range of what harmonic?
- second harmonic (H2) of the CF-component.
40
Doppler Shift Compensation
- challenge: bats auditory system is most sensitive to a specific frequency range ("sweet spot").
- solution is the bat compensates by lowering the frequency of its call as it flies towards the perch. This makes sure that the returning echo remains in the frequency range where its auditory system is the most sensitive.
- as the bat gets closer to perch, it adjusts the call frequency less and less because the doppler shift effect diminishes with decreasing speed.
41
How does the neuron's in the auditory system of bats process echoes and doppler shifts? how are the frequency shifts and delay processed in the brain?
- auditory cortex of bat.
- darkness and thickness of the line represents the relatively amplitude of the harmonics (CF2/FM2 and CF3/FM3 are louder than CF1/FM1)
- the flat part of the bats call represents a constant frequency (CF)
- the tail of the call is the frequency modulated (FM) part, where the frequency skips over a range.
42
Neurons in the Auditory Cortex
- many neurons in this region are specialized to process delays & shifts in pitch between the FM components, particularly between:
FM1
FM3
- when played together, echo delay is 2-4 ms, neurons fire maximally. playing alone does not strongly activate.
different parts within each FM1-FM3 column contain neurons that are sensitive to different FM1 and FM3 combinations.
- fundamental frequency (FM1) of a bats call is much quieter than higher harmonics (FM2 and FM3)
- FM1 can be easily masked by background noise, especially in crowded environment.
43
Is FM1 specific to the calling bat?
Yes
- in a group of bats, FM1 frequency of a bat's own call is best heard by the calling bat itself, as FM1 attenuates more rapidly over the distance than FM2 and FM3.
- FM2 and FM3 are stronger in amplitude, provide louder echoes/calls.
44
Describe the comparison between comparing FM1-FM3 and FM1-FM2?
- comparing FM1 of the call to FM2 or FM3 of the echo allows bat to process clearer, stronger signals.
(1) comparing FM1-FM3:
- timing-related task.
- likely specialized for timing discrimination (e.g., echo delay)
- FM3 is louder, easier to detect in the echo, making it more reliable for calculating the precise time delay between the pulse and the echo.
(2) comparing FM1-FM2:
- frequency determining task.
- may contribute more to frequency discrimination and fire-tuning of motion analysis, as FM2 and FM3 echoes provide stronger doppler shift information than FM1.
This division of labor ensures the bats auditory system can process complex echolocation data efficiently and accurately.
45
What is vocal learning?
The ability to imitate and reproduce sounds (used for communication)
46
What are the behavioral/cognitive processes involved in vocal learning?
(1) Sensory learning (for vocal learning):
- Memorize the sounds that need to be produced (i.e., form a sensory “template” or memory)
(2) Sensorimotor learning (for vocal learning:
- Learn how to produce the memorized sounds (i.e., figure out the motor program to produce an accurate imitation of the learned song).
47
What is the most studied species on vocal learning? What did we learn?
- Finches bird
- They hatch
- 0-25 days: sensory (critical period for sensory learning)
- 60-90 days: sensorimotor
- adult: crystallized (song mature stereotyped song)
48
Song Development in Zebrafish
- motif (5 different acoustic elements that we call syllabus).
- 'blabbling' -> stereotyped songs (that is an accurate imitation of their tutor song)
- learn a lot from thier fathers song.
- song of a bird is 99% due to experience (like how humans are with language)
- evolutionary distribution of vocal learning in birds
- distribution of vocal learning in mammals.
49
Describe the process of sensory learning (memorize sounds that need to be produced)
- NCM (caudomedial nidopallium): auditory processing area in forebrain that is important for auditory learning.
- before tutoring, NCM neurons respond to the sounds of various songs.
- after tutoring, NCM neurons respond selectively activated by songs of their tutor.
- neurons in the NCM are shaped by auditory learning and some neurons in NCM become specifically tuned to the tutor's song.
- when testing, want to look at adult song, not as variable. by manipulating neural activity inNCM (with drugs like UO126, a MAPK/ERK pathway inhibitor), researchers observed disrupted learning of the tutor song.
- when neural activity in NCM was disrupted during testing, birds initiated song had fewer tutor-like symbols.
50
HVC
- sensorimotor area
- brain region involved in both auditory processing and motor control of song production
- critical role in integrating sensory (auditory) information with motor commands needed for vocal learning.
- function is analogous to mammalian premotor cortex (broca's area) involved in motor/speech areas.
51
What are HVC and NCM areas critical for?
- HVC and NCM are critical for sensory learning of a tutor's song.
- HVC: essential for forming a neural representation of tutors song and integrating auditory and motor aspects of learning.
- NCM: processes and encodes auditory memories of the tutors song during exposure.
- disrupting HVC activity during tutoring impairs the Jevunilles birds ability to accurately initiate the tutors song.
- HVC neurons are tuned to respond most strongly to the tutor's song compared to other auditory stimuli.
- uninterupted HVC activity is necessary for accurate learning of specific song components.
52
What is the model for sensorimotor learning in the service of local learning?
- Sensory learning = formation of "song template"
-> then evaluate the feedback relative to the song template -> song control nuclei -> song -> auditory feedback -> back to evaluating.
Simplified model:
(1) Song template (memorized song)
adaptive modifications to motor commands for song; gradual modification of song across development
(2) Neural circuits for vocal performance
the sound of the vocalizations generated from the motor commands are compared to song template using auditory feedback; mismatch ("error") computed.
- Reward (strengthen) the motor commands that produce “good renditions of song.”
- Punish (weaken) the motor commands that produce “bad” renditions of song.
53
What are the song-learning phases in White-Crowned Sparrows?
(1) Sensory learning Phase.
- during spring of their first year.
- song stored as LTM but not immediately practiced.
(2) Sensorimotor learning phase.
- 6-9 months later.
- Juvenilles engage in 'blabbling', experimental vocalizations, imitating songs stored in memory.
- process shows LTM storage and recall, as sparrows retain memorized songs for months before practicing them.
54
Why are auditory feedbacks important?
- critical for accurate song development, experiments have shown that sparrows deafened before practicing songs fail to develop species-typical songs.
- even though birds memorize tutor songs during sensory phase, lack of auditory feedback prevents them from refining and correcting their vocalizations during sensorimotor phase.
- sparrows in different populations, develop different dialects reflecting regional / variations in song learning.
55
Neuromodulation and Dopamine's Role in Song Learning
- dopamine is made by dopaminergic neurons in the ventral tegmental area (VTA).
- dopaminergic neurons express tyrosine hydroxylase, a key enzyme in dopamine synthesis.
- functions of dopamine: attention, reinforcement learning, motor control & sensory processing.
- VTA projects to Area X (major dopaminergic projections)
56
Area X
- specialized nucleus in the songbird brain.
- key for vocal plasticity and development.
- lesions area X during development prevents birds from producing a sterotyped song in adulthood (produced syllabuls in very different orders, variable sequence)
- VTA neurons that project to Area X is sensitive to variation in vocal performance.
- increased activity (spikes) on VTA-X neurons correlates with "better" vocal performance.
- dopamine release in Area X shapes both song development and performance refinement.
- stimulates dopamine acting as a reward signal, reinforcing behaviours associated with reward.
- manipulating dopamine release (either activation or inhibition) demonstrates its critical role in shaping behaviour through reinforcement and punishment mechanisms.
- lesions in area X prevent the stabilization of syllabul sequencing.
57
