Chapter 7 - Neuronal processing of sensory information

Question 1

Feature detectors

Answer 1

Neurons that respond selectively to specific features of a sensory stimulus

Question 2

Natural prey catching behavior of toads

Answer 2

• Consists of a series of well-defined individual behavioral patterns:
  – if recognizes predator either escape or freeze
  – if prey try to grab and eat it
• In the toad’s sensory world, prey are elongated objects that move in the direction of their long axis, while enemies/predators are objects that move in the direction of their short axis
  – Results in two behavioral responses –> worm-like and anti-worm-like

Question 3

Jorg-Peter Ewert (1938-)

Answer 3

• Wanted to know how toads recognize their prey
  – Determined that specific neurons in the retina respond selectively based on if prey or not (cannot identify the type of prey as they are not that specific)

Question 4

Feature detectors can be identified by…

Answer 4

Recording from the brain while exposing the animal to behaviorally relevant stimuli

Question 5

The major neural parts of the visual system of the toad

Answer 5

• The receptor cells and ganglion cells in the retina
• The optic nerve formed by axons of the ganglion cells
• The optic tectum and the thalamic-pretectal area

Question 6

Feature detectors for toads

Answer 6

• T5(2) neurons in the optic tectum show many properties that qualitfy them as feature detectors responding best to worm-like stimuli
  – T5(2) cells receive inhibitory input from the thalamic-pretectal area; this connection is thought to contribute to the enhancement of selectivity for features relevant for prey-enemy discrimination
  – Electrical stimulation of the optic tectum, believed to activate T5(2) neurons, elicits orienting movement in toads characteristic of prey-catching behavior

Question 7

Transorbital lobotomy

Answer 7

• Severs the connections to the prefrontal cortex in the frontal lobes of the brain
• Used to treat “mental health issues” at the time

Question 8

Walter Jackson Freeman (1895-1972)

Answer 8

Performed transorbital lobotomies

Question 9

Jose Manuel Rodriguez Delgado (1915-2011)

Answer 9

• Inserted electrodes into the hypothalamus to control aggression in bulls
  – Applied stimulation/electricity to reduce aggression
• People were afraid that this research could lead to complete governmental control

Question 10

Acute electrode

Answer 10

Is removed after the experiment; short-term

Question 11

Chronic electrode

Answer 11

Is place permanently or long-term

Question 12

Masakazu ‘Mark’ Konishi

Answer 12

• Studied barn owls
  – Their food consists of field mice and they hunt at night
  – Wanted to know how they localize their prey
  — Acoustic predators –> face is structured for hearing/funneling sound and one ear is higher than the other

Question 13

Barn owl prey localization

Answer 13

Can localize prey solely based on acoustic cues

Question 14

Azimuth

Answer 14

Horizontal plane in barn owl’s acoustic space

Question 15

Elevation

Answer 15

Vertical plane in barn owl’s acoustic space

Question 16

Barn owl sound localization

Answer 16

• The accuracy of sound localization, as indicated by a turning of the owl’s head toward the source of the stimulus, can be monitored by means of an electromagnetic angle-detector system
• Can locate sound with high accuracy in both azimuth and elevation

Question 17

Human vs barn owl sound localization

Answer 17

• Humans are good at localizing in the azimuth/horizontal plane (like barn owls), but they are not as good in the elevation/vertical plane
  – Elevation plays a critical role in a barn owl’s life (catching prey), but it doesn’t for humans, resulting in this difference

Question 18

Barn owl precision in both planes

Answer 18

1 to 2 degrees in both azimuth and elevation

Question 19

Barn owls analyze interaural time differences to locate sound in…

Answer 19

Azimuth

Question 20

Barn owls analyze interaural intensity differences to locate sound in…

Answer 20

Elevation

Question 21

Interaural time and intensity pathways

Answer 21

• Interaural time and intensity data are segregated in the first way stations processing auditory information
  – Neurons of the angular nucleus process intensity information
  – Neurons of the magnocellular nucleus respond to timing information

Question 22

Lloyd Jefferess’ model for detection of interaural time differences

Answer 22

• Interaural time differences are computed in the laminar nucleus
  – This is achieved by neurons of this nucleus functioning as coincidence detectors and axons arising from the magnocellular neurons as delay lines
• Coincidence –> waves are in sync and coincidence detector has maximal firing
• Noncoincidence –> waves are a little off-set and coincidence detector has weak firing
• Phase ambiguity –> waves from different phases are in sync, leading to max firing from coincidence detector

Question 23

Interaural intensity differences are computed in…

Answer 23

The posterior lateral lemniscal nucleus

Question 24

After parallel processing over several brain levels, time and intensity converge in the…

Answer 24

Lateral shell

Question 25

Space-specific neurons

Answer 25

Respond only to acoustic stimuli originating from a restricted area in space

Question 26

Through systematic arrangement of space-specific neurons…

Answer 26

A neural map of auditory space is formed in the external nucleus

Question 27

Auditory pathways in the brain

Answer 27

See diagram

Question 28

Baby barn owl fitted with prism glasses that deviate vision

Answer 28

• Owl sees the object a certain number of degrees away from the object’s actual location
• The connections that were already formed between auditory and visual pathways break down and are reformed due to the prism glasses, and when the glasses are removed the connections again need to be reformed
  – before glasses owl can see and hear perfectly
  – initially with the glasses owl can locate the object correctly with auditory data but sees it in the wrong place
  – overtime with the glasses owl locates and hear the object in the wrong place
  – after removing the glasses owl can see object in the right place but hears it in the wrong place

Question 29

In the optic tectum…

Answer 29

A joint auditory-visual map is formed