Download Auditory Cortex

PowerPoint Presentation for
Biopsychology, 8th Edition
by John P.J. Pinel
Prepared by Jeffrey W. Grimm
Western Washington University
Copyright © 2011 Pearson Education,
Inc. All rights reserved.
This multimedia product and its contents are protected
under copyright law. The following are prohibited by law:
• any public performance or display, including
transmission of any image over a network;
• preparation of any derivative work, including the
extraction, in whole or in part, of any images;
• any rental, lease, or lending of the program.
Chapter 7: Mechanisms of
Perception: Hearing, Touch,
Smell, Taste, and Attention
How You Know the World
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Principles of Sensory System
Organization

Primary – input mainly from thalamic relay nuclei



For example, striate cortex receives input from
the lateral geniculate nucleus
Secondary – input mainly from primary and
secondary cortex within the sensory system
Association – input from more than one sensory
system, usually from secondary sensory cortex
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Principles of Sensory System
Organization Continued

Hierarchical Organization





Specificity and complexity increases with each
level
Sensation – detecting a stimulus
Perception – understanding the stimulus
Functional Segregation – distinct functional
areas within a level
Parallel Processing – simultaneous analysis
of signals along different pathways
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
FIGURE 7.1 The hierarchical
organization of the sensory systems.
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
FIGURE 7.2 Two models of sensory system
organization: The former model was
hierarchical, functionally homogeneous, and
serial; the current model, which is more
consistent with the evidence, is hierarchical,
functionally segregated, and parallel.
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Auditory System



Natural sounds are complex patterns of
vibrations
A Fourier analysis breaks natural sounds
down into sine waves
There is a complex relationship between
natural sounds and perceived frequency
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
FIGURE 7.3 The relation between the
physical and perceptual dimensions of
sound.
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
FIGURE 7.4 The breaking down of a
sound—in this case, the sound of a
clarinet—into its component sine
waves by Fournier analysis.
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
The Ear


Sound waves enter the auditory canal of the
ear and then cause the tympanic membrane
(the eardrum) to vibrate
This sets in motion the bones of the middle
ear, the ossicles, which trigger vibrations of
the oval window
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
The Ear Continued



Sound wave > eardrum > ossicles (hammer,
anvil, stirrup) > oval window
Vibration of the oval window sets in motion
the fluid of the cochlea
The cochlea’s internal membrane, the organ
of Corti, is the auditory receptor organ
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
FIGURE 7.5 Anatomy of the ear.
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
The Ear Continued

The organ of Corti is composed of two
membranes



Basilar membrane – auditory receptors, hair cells,
are mounted here
Tectorial membrane – rests on the hair cells
Stimulation of hair cells triggers action
potentials in the auditory nerve
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
The Ear Continued



Cochlear coding:
Different frequencies produce maximal
stimulation of hair cells at different points
along the basilar membrane
Tonotopic (frequency) organization of the
basilar membrane and most other auditory
system components
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
From the Ear to the Primary
Auditory Cortex





The axons of each auditory nerve synapse in the
ipsilateral cochlear nuclei
From there, many projections lead to the superior
olives on both sides of the brain stem
From there, axons project via the lateral lemniscus
to the inferior colliculi
Axons then project from the inferior colliculi to the
medial geniculate nuclei of the thalamus
Thalamic neurons then project to the primary
auditory cortex
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
FIGURE 7.6 Some of the pathways
of the auditory system that lead
from one ear to the cortex.
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Subcortical Mechanisms of
Sound Localization

The lateral and medial superior olives react
to differences in what is heard by the two
ears



Medial – arrival time differences
Lateral – amplitude differences
Both project to the superior colliculus

The deep layers of the superior colliculus are laid out
according to auditory space, allowing location of sound
sources in the world; the shallow layers are laid out
retinotopically
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Auditory Cortex



Auditory cortex is located in the temporal lobe
Core region: includes primary cortex
Belt surrounds the core region



A band of secondary cortex
Secondary cortex outside the belt referred to
as parabelt areas
About ten seperate areas of secondary
auditory cortex in primates
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
FIGURE 7.7 General location of the
primary auditory cortex and areas of
secondary auditory cortex.
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Organization of Primate
Cortex



Functional columns (cells of a column respond
to the same frequency)
Tonotopic organization-is the spatial
arrangement of where sounds of different
frequency are processed in the brain.
Secondary areas do not respond well to pure
tones and have not been well-researched
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
What Sounds Should Be
Used to Study Auditory
Cortex?



There is a lack of understanding of the
dimensions along which auditory cortex
evaluates sound
All through the cortical levels of the auditory
system there are cells that respond to
complex sounds
Perhaps study with pure tones is limited
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Two Streams of Auditory
Cortex

Auditory signals are conducted to two areas
of association cortex




Prefrontal cortex
Posterior parietal cortex
Anterior auditory pathway may be more
involved in identifying sounds (what)
Posterior auditory pathway may be more
involved in locating sounds (where)
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
FIGURE 7.8 The hypothesized anterior
and posterior auditory pathways.
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Auditory-Visual Interactions

There is evidence for interactions between
the auditory and visual systems


e.g. some posterior parietal neurons with both
visual and auditory receptive fields
Interaction in primary sensory cortices
indicate that sensory system interaction is an
early and integral part of sensory processing
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Where Does the Perception
of Pitch Occur?


Most auditory neurons respond to changes
in frequency rather than pitch
One small area just anterior to primary
auditory cortex has neurons that respond to
pitch rather than frequency

May be where frequencies of sound are
converted to perception of pitch
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Effects of Damage to the
Auditory System
Lesions of auditory cortex in rats results in
few permanent hearing deficits
Lesions in monkeys and humans hinder
sound localization and pitch discrimination
Deafness in humans



Total deafness is rare, due to multiple pathways
Two kinds: conductive deafness (damage to
ossicles) and nerve deafness (damage to
cochlea)



Partial cochlear damage results in loss of hearing at
particular frequencies
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Somatosensory System:
`
Touch and Pain




Somatosensory system is three separate and
interacting systems:
Exteroceptive – external stimuli
Proprioceptive – body position
Interoceptive – body conditions (e.g.,
temperature and blood pressure)
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Cutaneous Receptors

Free nerve endings


Pacinian corpuscles





Temperature and pain
Adapt rapidly, large and deep; onion-like
Respond to sudden displacements of the skin
Merkel’s disks – gradual skin indentation
Ruffini endings – gradual skin stretch
Dermatome – the area of the body innervated by
the left and right dorsal roots of a given segment
of spinal cord
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
FIGURE 7.10 Four cutaneous
receptors that occur in human
skin
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Two Major Somatosensory
Pathways

Dorsal-column medial-lemniscus system



Mainly touch and proprioception
First synapse in the dorsal column nuclei of the
medulla
Anterolateral system



Mainly pain and temperature
Synapse upon entering the spinal cord
Three tracts – spinothalamic, spinoreticular,
spinotectal
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
FIGURE 7.12 The dorsalcolumn medial-lemniscus
system.
FIGURE 7.13 The anterolateral
system.
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Cortical Areas of
Somatosensation

Primary somatosensory cortex (SI)




SII – mainly input from SI


Postcentral gyrus
Somatotopic organization (somatosensory
homunculus) – more sensitive, more cortex
Input largely contralateral
Somatotopic; input from both sides of the body
Much of the output from SI and SII goes to
association cortex in posterior parietal lobe
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Effects of Damage to the
Primary Somatosensory
Cortex

Effects of damage to the primary
somatosensory cortex are often mild

Likely due to numerous parallel pathways
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Somatosensory System and
Association Cortex


Highest level of sensory hierarchy are
areas of association cortex in prefrontal
and posterior parietal cortex
Posterior parietal cortex contains bimodal
neurons


Neurons that respond to activation of two
different sensory systems
Allow integration of visual and somatosensory
input
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Somatosensory Agnosias

Astereognosia – inability to recognize objects
by touch


pure cases are rare – other sensory deficits are
usually present
Asomatognosia – the failure to recognize
parts of one’s own body (the case of the man
who fell out of bed)
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Perception of Pain



Despite its unpleasantness, pain is
adaptive and needed
No obvious cortical representation of
pain (although the anterior cingulate
gyrus appears involved in the emotional
component of pain)
Descending pain control – pain can be
suppressed by cognitive and emotional
factors
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Descending Pain Control




Circuitry identified by the following studies:
Electrical stimulation of the periaqueductal
gray (PAG) has analgesic effects
PAG and other brain areas have opiate
receptors
Existence of endogenous opiates (natural
analgesics) – endorphins
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
FIGURE 7.18 Basbaum and
Fields’s (1978) model of the
descending analgesia circuit.
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Neuropathic Pain



Severe chronic pain in the absence of a
recognizable pain stimulus
Likely from pathology of nervous system
linked to an injury
Some evidence for aberrant glial cell
signals triggering neural pain pathways
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Chemical Senses: Smell and
Taste

Olfaction (smell)


Gustation (taste)


Detects airborne chemicals
Responds to chemicals in the mouth
Food acts on both systems to produce flavor
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Chemical Senses: Smell and
Taste






Pheremones are chemicals that influence that
behavior of conspecifics (members of the same
species)
Evidence of human pheromones
Changes in olfactory sensitivity across and
menstrual cycle
Synchronization of menstrual cycles
Sex identification by smell (especially by women)
Men can identify menstrual stage by smell
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Olfactory System


Receptor cells embedded in the olfactory mucosa of
the nose
Many different kinds of receptors



Same kinds of receptor cells project to similar areas
of the olfactory bulb


Rats and mice have about 1,500
Humans have almost 1,000
clusters of neurons near the surface of the olfactory bulbs
 olfactory glomeruli
New receptor cells are created throughout life
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Olfactory System Continued

Olfactory tract projects to several structures
of the medial temporal lobes including
amygdala and piriform cortex


does NOT first pass through the thalamus
only sensory system that does this
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
FIGURE 7.19 The human
olfactory system.
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Gustatory System

Receptors in tongue and oral cavity in clusters
of about 50 called taste buds




located around small protuberances called papillae
> 4 (sweet, sour, salty, bitter) primary tastes –
5th is umami, meat or savory
Many tastes not created by combining
primaries
Salty and sour don’t have receptors; they
merely act on ion channels
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Gustatory System Continued



Gustatory afferent neurons leave the mouth as
part of the 7th, 9th, and 10th cranial nerves to the
solitary nucleus of the medulla
Projections then pass to the ventral posterior
nucleus of the thalamus
From there, neurons project to the primary
gustatory cortex and then to the secondary
gustatory cortex
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
FIGURE 7.20 Taste receptors,
taste buds, and papillae on the
surface of the tongue.
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Brain Damage and the
Chemical Senses

Anosmia – inability to smell



Most common cause is a blow to the head that
damages olfactory nerves
Incomplete deficits seen with a variety of
disorders
Ageusia – inability to taste

Rare due to multiple pathways carrying taste
information
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Selective Attention


Improves perception of what is attended to
and interferes with that which is not
Internal cognitive processes (endogenous
attention) and external events (exogenous
attention) focus attention
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Selective Attention Continued

Cocktail-party phenomenon – indicates that
there is processing of information not
attended to
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Change Blindness

Change blindness – no memory of that
which is not attended to

We do not appear to remember parts of a
scene that are not the focus of our attention
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Neural Mechanisms of
Attention


Selective attention is thought to work by
strengthening the neural responses to
attended-to aspects and by weakening the
responses to other
For example, spatial attention can shift the
location of receptive fields (Wommelsdorf
et al. 2006)
Copyright © 2011 Pearson Education, Inc. All
rights reserved.
Simultanagnosia

Simultanagnosia – a difficulty attending to
more than one visual object at a time

Typical cause: bilateral damage to the dorsal stream
(involved with localizing objects in space)
Copyright © 2011 Pearson Education, Inc. All
rights reserved.