Lecture 4 (Prof. Scheifele)

Marine Mammal Bioacoustics: The Central Auditory System

Peter M. Scheifele MDr, PhD, LCDR USN (Ret.)University of Cincinnati

Communication Sciences and Disorders, Neuroaudiology Dept.University Medical Center

scheifpr@uc.edu

Central Nervous System1. Consists of: spinal cord & brain

spinal cord • conducts sensory information• conducts motor information The brain • receives sensory input from the spinal cord and cranial nerves• devotes most of its volume (and computational power) to processing its

various sensory inputs and initiating appropriate — and coordinated — motor outputs.

From: asymptotia.com/wp-images/2007/08/ 3CSD 512 L1

The Brain- by System

• Reptilian brain• Limbic system• Neocortex

From: spinwarp.ucsd.edu/NeuroWeb/Text/br-800epi.htm and http://www.ascd.org/portal/site/ascd/template.chapter/menuitem.b71d101a2f7c208cdeb3ffdb62108a0c/?chapterMgmtId=effbcba5ddcaff00VgnVCM1000003d01a8c0RCRD

From: http://www.crystalinks.com/reptilianbrain.html 4CSD 512 L1

Cerebral Cortex

• SULCI – shallow groove or depression

• FISSURE – a surface groove dividing and organ

• GYRI – Convolution of the brain surface separated by sulci

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cerebellum

Temporal

Frontal

ParietalOccipital

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The Cerebrum: Ascending auditory system from thalamic to cortex- or…Gray

matter over white matter…What’s the matter?

Deep-lying structures: Basal ganglia; amygdala; hippocampus

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More Gross Anatomy (Exterior)Supramarginal

Gyrus

Auditory

Visual

Somesthetic

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Synaptic Vesicle

Receptors

Autoreceptors

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BRAINS OF VARIOUS ANIMALS

ANIMAL

BRAIN WEIGHT (G)BRAINWEIGHT

BODY WEIGHT % BODY WT

SPERM WHALE 7800 g15 tons=30,000 pounds= 13500 kg

0.06 %

ELEPHANT 6000

BOTTLE-NOSED DOLPHIN 1500 g 500 kg 0.3 %

HUMAN ADULT 1300-1400 150 pounds= 68 kg=68000 g 2 %

HORSE 532

CHIMPANZEE 420

HUMAN BABY 350 - 400

DOG (BEAGLE) 72 9 to 18 kg 0.5 %

CAT 30

SQUIRREL 22

ALLIGATOR 8.4 250 kg 0.003 %

OWL 2.2

RAT 2 400 gm 0.5 %

TURTLE 0.3

VIPER 0.1

GREEN LIZARD 0.08

540 kg

10,000

Cranial Nerves

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Cranial Nerves

Images from: /www.med.umich.edu/lrc/coursepages/M1/anatomy/html/atlas/images/

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Classification of NervesDivided into Sensory and Motor divisions

Sensory (afferent) nerves

Motor (efferent) nerves

Mixed nerves

Image from: www.merck.com/mmhe/sec06/ch077/ch077c.html16CSD 512 L1

The Central Auditory Nervous System (CANS)

• Sound localization and lateralization• Auditory discrimination

– Frequency discrimination– Intensity discrimination– Quality (timbre)

• Pattern recognition• Temporal discrimination

– temporal resolution,– temporal masking, – temporal integration, – temporal ordering

• Auditory performance in presence of competing signals• Auditory performance in the presence of degraded signals

Acoustical Roles of the Brain

• Processing of sound– Localization– Temporal discrimination– Intensity discrimination– Frequency discrimination

• Vocalization development– Motor functions for vocalization– Sound ordering and development

• Communication and maybe language

Ear and Brain are BOTH Required for Hearing

• Brain is also tonotopically organized• Brain performs acoustic processing functions– Discrimination– Localization– Patternization

• Brain makes use of the processed sound– Links to memory and understanding

• Fight or flight• Language• Vocalization links

Brain Comparison

Central Auditory Pathways

Medulla

Pons

Thalamus

MGB

Inferior Colliculus

Region of Cochlear Nucleus

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The cochlear nuclei

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TRAPEZOID BODY

The trapezoid body calculates interaural intensity differences

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LATERAL LEMNISCUS

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The inferior colliculus: processes sounds for auditory perception and reflex adjustments

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The brachium of the inferior colliculus and the medial geniculate nucleus

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2 – inferior colliculus

18 – brachium of the inferior colliculus

21- medial geniculate body

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Transverse temporal gyri

SOME GROSS OBSERVATIONS

• Large, unusually shaped

• Well-fissured• Olfactory bulbs absent• Radical hypertrophy of

acoustic areas

BRAIN STRUCTURES: Possible Neurological Meaning

• Is relative size of specific areas a definite expression of the importance of its principal function?

• Past slide preparations of non-perfused brains have given only limited data regarding architectural arrangements of the cortex.

• Recent advances in anesthesia have allowed brains to be perfused in situ for histoarchitectural studies.

Auditory Cortex

Cetacean Auditory Anatomy

Image from: http://instruct1.cit.cornell.edu/courses/bionb424/students2004/kls36/neuroanatomy.htm

Comparative Auditory Anatomy

• Auditory brainstem nuclei and corresponding fiber diameters much larger than human equivalents

• Auditory structures are also much larger in odontocetes than mysticetes

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