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The Stimulus for addition

§ Sounds are vibrations of air molecules that are produced by objects.
§ If the vibration ranges between 30 and 20,000 times per second, it
stimulates receptor cells in the ears
Sound has three physical dimensions:
- The pitch determines the frequency
of the molecular vibrations. It is measured in hertz (Hz) or cycles per second.
- The loudness corresponds to the amplitude or intensity of the molecular vibrations.


Anatomy of the Ear

Sound is funneled through the pinna (the external ear)
Sounds coming down the ear canal cause the tympanic membrane (the eardrum) to vibrate. These vibrations are transferred to the middle ear
The middle ear comprises three ossicles (small bones of the middle ear: the malleus, incus and stapes
The cochlea is part of the inner ear. It is a long coiled tube structure containing fluid. It also contains the receptors.

Ear does not mix soundewaves, Auditiry system does.


Cross Section Through Cochlea

The cochlea is divided into three longtudinal divisions: scala vesibuli, scala media and scala tympani
The receptive organ is the organ of Corti. It consists of the basilar membrane, the tectorial membrane and hair cells

The hair cells are the auditory receptors.
Fine cilia extensions of the hair cells attach to the tectorial membrane
Sound waves cause the basilar membrhane to move relative to the tectorial
membrane which bends the cilia of the hair cells. This bending of the cilia produces receptor potentials
(For more detail, see pages 214-218 of textbook)


Auditory transduction

(For more detail, see pages 214-218 of textbook)


From the Ear to the Primary Auditory Cortex

1. The organ of Corti sends auditory information to the brain by the cochlear nerve.
2. The axons enter the cochlear nuclei where they synapse.
3. The axons of the cochlear nuclei then enter the superior olivary complex.
4. Axons from superior olivary complex pass through a bundle of fibres (lateral lemniscus) and enter the inferior colliculus.
5. The axons then pass to the medial geniculate nucleus of the thalamus which make their way to the primary auditory cortex of the temporal lobe.


Tonotopic Representation
Topography: features and landscapes, in this case of sound frequency and anatomy.

§ The major principle of cochlear coding is that different frequencies produce maximal stimulation of hair cells at different points on the basilar membrane.
§ Like the basilar membrane, the auditory cortex is also organised according to frequency, i.e. different parts of the auditory cortex respond best to different frequencies.
§ This organisation of different frequencies of sound that are represented in different places of the auditory cortex, is known as tonotopic representation.
Organization like this allows us to isolate sounds, localize too. Not sure how we filter all the noise, also activiting cells.


Perception of Complex Sounds
A principle function of the auditory system is to identify the sound.
§ Perception of complex sounds is accomplished by

neural circuits in the auditory cortex:must be specialized to preserve info

- axons have voltage-dependent potassium channels that
produce very short action potentials

- terminal buttons are large and therefore release large amounts of glutamate

- postsynaptic membrane contains neurotransmitter dependent ion channels which act rapidly and produce strong EPSPs

- terminal buttons synapse with the membrane of the soma of the postsynaptic neuron. This minimizes the distance between the synapse and the axon

Makes things gi zippy (fast)


The Primary Auditory Cortex

The Primary Auditory Cortex
§ The primary auditory cortex is hidden on the upper bank of the lateral fissure.
§ The belt region is the first level of auditory association cortex.
§ The parabelt region is the second level of auditory association cortex.

Core, belt parables.
Hierarchy, like vision.
To topic representation.
Levels of analysis of auditory info start here.


The “What” and “Where” Streams: Where Vision and Audition Converge

Dorsal stream - terminates in the posterior parietal cortex. Involved in sound localisation (“where”)
Ventral stream - terminates in the temporal lobe. Involved with analysis of complex sounds (“what”)
Overlap shows how we use both vision and auditory to understand sounds and sights. In conjunction, convergence. Processing problem solving. Suggests convergence sight and sound, imp. Aspects of high order cognitive processing.


Perception of Music requires,
Yogita like opera.

§ Music is a special and complex form of auditory processing
§ Particular combinations of musical notes can be perceived as
happy, sad, pleasant, unpleasant, consonant, dissonant, etc.
§ Music perception requires:
- recognition of sequences of notes,
- rules that govern permissible pitches,
- rhythmic structure,
- memory capacity

Partly culturally determined.


Different regions of the brain are involved in different aspects of musical perception:

- recognition of harmony - inferior frontal cortex
- underlying beat - right auditory cortex
- rhythmic patterns superimposed on the rhythmic beat - left auditory cortex
- musical timing and movements - cerebellum and basal ganglia


Recognition of complex auditory sounds (Lewis et al., 2004)

§ Presented subjects with “recognisable” recordings of environmental sounds (e.g. tools, pouring liquids, dropping objects) - activated region of the ventral stream
§ Sounds were presented backwards as well (preserved complexity but difficult to recognise) - does not activate auditory cortex. ParticulR ventral pathway specific to audition, just for recognition of sounds,
Means we have an auditory memory,
No animal model of.



§ After sustaining brain damage, patient I.R. developed complete amusia, the inability to perceive or produce melodic music.
§ She could recognise different emotions expressed in music.
§ She could also recognise environmental sounds, converse and
understand speech.
§ However, she was unable to tell the difference between consonant (e.g. harmony; pleasant sounding) and disonante (unstable, transitional) music.


Birdsong: Auditory Communication in Birds

Birds raised in different regions acquire different dialects
Songbirds, hummingbirds and parrots.
Bats and whales and dolphins only other mammals,
Communicate using "voice"

Song used for, attention, mating, danger?
Eearly upbringing leads to learning of language.

Birdsong and humans language have broad simialriities.
Innate similar in enviorment.
Complexity vary.
Type and elements employed like syllables differ.
Patterns of speech sounds.

So it make an intereting and hot area of study.

Neurobiology of birdsong.
Organization of brain structures for vocal learning.

Emotion in marmates monkey too.

Hmm study cat vocal calls to humans. That would be fun! Meal time meow!

Birds may help with genetic and speech impairments and disorders brain issues.


Echolocation: Auditory Communication in Bats

§ Echolocating bats use sound waves to navigate, hunt and communicate.
§ Echolocation works like a sonar; the bat navigates by the echoes that it hears.
§ A bat with a 40cm wingspan can navigate through openings in a 14 x 14 cm mesh made from very fine nylon thread while flying in total darkness.

Bats have cochlea fovea, frequency range for doc location more neurons, cortex specialized Eco inputs.
Distance, location, oeitentTion, velocity,
Night to Eco vision.

Sheds light into how we use audition to navigate the world.
Goodale Eco location for visually impaired!


three interacting somatosensory systems:?

§ Somatosenses provide information about what is happening on the surface of the skin and inside it.
§ There are three interacting somatosensory systems:
- the exteroceptive system senses external stimuli applied to
the skin (e.g. touch)
- the proprioceptive system monitors information about the
position of the body and its posture (e.g. kinesthesia)
- the interoceptive system provides information about conditions within the body (e.g. blood pressure)


The Stimulus forsomatosenses (exteroceptive)

§ The cutaneous senses (skin senses) respond to different types
of stimuli:
- vibrations occur when we move our fingers across a rough surface
- pressure is caused by mechanical deformation of the skin
- temperature is produced by objects that heat or cool the
- pain is caused by events that cause tissue damage


Anatomy of the Skin
Hairy sin, or non hair glabrous skin

Ruffini corpuscles are sensitive to light touch, skin stretch and kinesthetic sense of finger position and movement
The dermis and epidermis make up two layers of subcutaneous tissue. Receptors are scattered throughout these layers
Merkel’s disks respond to skin indentations
Glabrous skin is ‘hairless’ skin (e.g. fingertips, foot soles, hand palms)
Meissner’s corpuscles respond to low frequency vibrations (e.g. taps on the skin)
Pacinian corpuscles respond to skin vibrations. They consist of a concentric layers wrapped around dendrite of a single axon


From the Skin to the Primary Somatosensory Cortex The Somatosensory Pathway

Axons from the skin, muscles and internal organs enter the CNS via spinal nerves (e.g. dorsal root ganglia).
1. Localised information (e.g. fine touch) ascends through the dorsal column of the white matter of the spinal cord and enter the medial lemniscus via the medulla.
2. The axons ascend to the ventral posterior nucleus of the thalamus and project to the primary somatosensory cortex
3. Nonlocalised information (pain or temperature) enter the spinal cord, cross to the other side and ascend through the spinothalamic tract.

So auditory info switches sides early on, senses later on.
Ipsilateral start for sensory
Pain contro lateral though?


The Somatosensory Homunculus (Penfield et al., 1937)

§ Penfield applied electrical stimulation to various sites on the somatosensory cortical surface.
§ Patients reported somatosensory sensations in various parts of their bodies

Patients reported somatosensory sensations in various parts of their bodies
§ The relationship between the cortical stimulation and the body part sensation produced a somatotopic map of the body surface
§ The somatopic map is also referred to as the somatosensory homunculus (“little man”)


Somatosensory Agnosia

Patients with tactile agnosia cannot identify objects by touch
§ Patient E.C. has left parietal lobe damage. She cannot recognise common objects: - pine cone > brush
- ribbon > rubber band - snail shell > bottle cap
§ Patient M.T. can draw objects when touched but he cannot recognise them


Perception of Pain
Could be argued a very personal experience but here are some def. and other info.

- “An unpleasant sensory and emotional experience associated with
tissue damage or described in terms of tissue damage” (International Association for the Study of Pain).
- “Pain is whatever the experiencing person says it is; existing whenever he or she says it does” (MaCaffery, 1972).
- “Pain is a category of complex experiences, not a single sensation produced by a single stimulus” (Melzack and Wall, 1982).
§ Pain can be modified by opiates, hypnosis, placebo’s, acupuncture, etc
§ Pain is vital for survival in humans and animals.

Pain makes us avoid further damage to body, not o something again that hurts, help us heal.


Brain Mechanisms of Pain

The unpleasantness component refers to the degree to which the individual is bothered by the pain. Mediated by pathways leading to the anterior cingulate and insular cortex
The component of long term implications represents one’s future comfort and well-being.
Mediated by pathways that reach the prefrontal cortex
Sensory component
concerned with pure perception of the intensity of a painful stimulus. Mediated by a pathway from spinal cord to the somato- sensory cortices via the ventral posterior thalamic nucleus

See the diagram!


Evidence for Brain Mechanisms of Pain (Rainville et al., 1997)

Subjects placed their hands in ice cold water to produce a pain sensation
§ Subjects with hypnosis reported less unpleasant pain even though the pain was still intense.
§ Brain activations were observed in a PET scanner
§ Painful stimuli increased activation in both anterior cingulate cortex and primary somatosensory cortex.
§ When hypnotized, anterior cingulate activity “decreased” and activity of somatosensory cortex remained “high.”
§ Somatosensory cortex involved in pain perception. Anterior cingulate is involved in immediate emotional effect.


Phantom limb (Melzak, 1992)

§ Phantom limb is a form of pain sensation that occurs after a limb has been amputated.
§ Amputees report that the missing limb still exists and that it often hurts.
§ It is thought that phantom limb sensation is due to the cut axons belonging to the amputated limb. These cut ends cannot be reestablished and form nodules called neuromas.
§ An alternative explanation is that the problem is inherent in the organisation of the parietal lobe. The parietal lobe is involved in the awareness of one’s own body. People with damage to the parietal lobe have been known to push their leg out of bed because they think it belongs to someone else (Melzack, 1992)


Pain Perception and Environmental Stimuli

§ A variety of environmental stimuli can activate analgesia-producing circuits
§ Electrical stimulation of the periaqueductal gray matter (in midbrain) causes the release of endogenous opioids.
§ Acupuncture, but not hypnosis, causes release of endogenous opioids.


Biological Significance of Analgesia

§ Suppression of pain during behaviours (e.g. fighting)
§ Helps us deal with unavoidable pain


From textbook skin parts functions

Merkel’s disks provide information about form and roughness, especially to the finger-tips. Ruffini corpuscles provide information about static forces to the skin and about stretching of the skin, which contributes to kinesthetic feedback. Meissner’s corpuscles provide information about edge contours and to Braille-like stimuli, especially to the fingertips. Pacinian corpuscles provide informa-tion about vibration, especially that detected by con-tact by the ends of elongated objects such as tools with other objects. Painful stimuli and changes in temperature are detected by free nerve endings