Download Neurobiology of Behaviour

Neurobiology of Behaviour:
The mechanisms underlying an animal’s response
to its environment
Dr Alice Witney
Department of Physiology
[email protected]
http://www.medicine.tcd.ie/physiology/courses/student_area/
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Dr Alice Witney
Comparative aspects of nervous systems
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Human brain has 10 12 neurons,
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The model systems approach
simpler nervous systems
ecological specialisms
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Brain
Spinal
Cord
Molecular and Cellular similarities:
Invertebrate and Vertebrate nervous
systems share properties at a
molecular and cellular level
(eg neurotransmitters)
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Morphological differences:
Vertebrate: spinal cord and brain
Invertebrate: segmental nervous system
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Dr Alice Witney
Brain Thoracic
Abdominal
Typical Neuron
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Neurons:
Cells specialized for
processing and
transmitting
information
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Sensory Neurons:
Neurons that are
specialized to
respond to the
environment
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Motor Neurons:
Neurons that have
axons terminating on
muscle fibres
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Interneurons: All the
other forms of
neurons
INPUT
Receiving signals
The Action
Potential
OUTPUT
Sending signals
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Dr Alice Witney
Neurobiology of Animal Behaviour
• Moving in the environment:
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The Leech: Understanding the neural basis for rhythmic movements like locomotion
• Learning and adapting to the environment:
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The cellular basis for changes in behaviour during learning.
Hebb (1949): Repetitive activity at a synapse could produce lasting cellular
changes
Aplysia: Habituation and Classical Conditioning (in the tradition of Ivan Pavlov)
• Sensing the environment:
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The barn owl: Learning to locate prey, formation and plasticity of an auditory map
The weakly electric fish: Electric signals to detect objects in the environment
• Spatial Navigation:
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Changes in brain volume after spatial tasks
• Control of the Hand:
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Primates, the opposable thumb, and development of underlying control
• Collective Behaviour:
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Swarming in Locusts
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Dr Alice Witney
Behaviour is Movement:
Central Pattern Generators
The Medicinal Leech
Hirudo medicinalis
Central pattern generators (CPGs) :
• neural circuits that generate periodic motor
commands for rhythmic movements like
locomotion, swimming, flight, breathing
• can occur in the absence of sensory
feedback, but are „shaped‟ by sensory
input
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Dr Alice Witney
Following a rhythmic movement: frameby-frame analysis of swimming
Hirudo medicinalis as a model system for
understanding CPGs
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•
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An accessible nervous system
A repetitive behaviour, the CPG can be initiated in isolated ganglia
An easily elicited behaviour
Understanding of CPGs important comparatively across species
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Dr Alice Witney
The Leech: Model systems and Identified
Neurons
Staining of an identified
neuron in the Leech
An identified neuron is
one that is recognizable
as it occurs in the same
location and has the
same function in every
member of a species
P, T, N, Rz cells
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Dr Alice Witney
Aplysia californica : A model system for
learning and memory
Kandel, E.R. (2001) Science Vol 294 pp 1030-1038
Aplysia californica,
The sea hare
• Relatively simple nervous system (20,000 neurons)
• Large (up to 1 mm in diameter) identified neurons
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Dr Alice Witney
• Neurons can be identified by position, size, colour and their
electrophysiological properties
Habituation in Aplysia
• Gill withdrawal reflex
occurs when the siphon
or mantle shelf is
stimulated.
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Dr Alice Witney
Understanding habituation at a cellular level
Abdominal Ganglion showing Identified
Neurons
•
http://neuronbank.org/
Intracellularly record
from identified sensory
neuron and identified
motor neuron
Record membrane
potential
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Dr Alice Witney
M
S
Habituation of a
tactile response
• Habituation could be
-Short term (minutes)
-Long term (hours to weeks)
Depression
at the
synapse
Response can be restored
through a strong electric
shock (sensitisation)
Behavioural change is
accompanied by changes in
the strength of the
monosynaptic
connections between the
sensory and motor neurons
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Dr Alice Witney
Changes in behaviour as a result of experience: non-associative learning
Classical Conditioning: Aplysia
CS (conditioned
stimuli) = Siphon
Stimulation
US (unconditioned
stimuli) = Tail Shock
CS+US
CS
UCR
CR
UR (unconditioned
response)= Siphon
Withdrawal
• Siphon withdrawal reflex
can be Classically
Conditioned
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Dr Alice Witney
Associative Learning: the learning of stimulusresponse relationships
Auditory Localization in the Barn Owl, Tyto alba
Knudsen, E.I. (2002) Nature Vol 417 pp 322-328
Sound waves
generated by
movements of a
mouse are
received by the
owl‟s left and right
ears.
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Dr Alice Witney
ITD
Space around
head relative to
line of sight
Interaural Time
Difference
Interaural Level
Difference
Plasticity of auditory localization in juveniles as a
prism vision
Behaviour:
Head
Orientation
to visual
(purple) and
auditory (red)
Before
Prisms
Day 1 visual
field displaced
to right
Day 42
Removal
8 wks
Neurobiology:
Influence on
neurons in Optic
Tectum
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Dr Alice Witney
Auditory and
Visual RF Aligned
prism
R ear leads
Plasticity
shown in the
projection from
ICC to ICX
(central nucleus of Inferior
Colliculus to external nucleus
of Inferior Colliculus)
Spatial
distribution of
labelled axons
for normal
juveniles and
prism reared
adults
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Dr Alice Witney
Sensory Processing: the weakly electric fish
Gnathonemus petersii
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How can sensory feedback from self-movement be distinguished from
sensory feedback from external source?
• The weakly electric fish generates electrical signals to probe the
environment.
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The electrolocation commands can be gated, amplified or predicted
in the brain by the fish return signal.
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Dr Alice Witney
Corollory Discharge enabling Sensory
Cancellation
• Gnathonemus petersii senses objects through the distortions they cause in an
electric field that it creates.
• Modifications to signal occur through corollary discharge mechanisms
• Similarity with the concept of “efference copy”
•Importance in distinguishing “self” from “other”
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Dr Alice Witney
Crapse & Sommer (2008) Nature Reviews Neuroscience Vol 9 pp 597-600
Neurobiology of Human Behaviours
• Neuropsychological Case Studies
• Patients with lesions in known brain areas
• Memory Deficits: The amnesic H.M. studied by Professor Brenda
Milner (hippocampal lesion; entorhinal cortex +)
• Phineas Gage – injured 1848 - function of the frontal lobe
Corkin (2002) Nature Reviews Neuroscience Vol 3 p153-160
Imaging has enabled
the site of brain
lesions to be
determined.
The influence of
damage to resulting
behaviour can then
be studied
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Dr Alice Witney
Reconstruction
of the accident
of Phineas
Gage
The hippocampus and spatial navigation
• Birds: brood
parasites, foodcaching
• Rats in mazes
• Human taxi drivers
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Dr Alice Witney
The Brown-headed Cowbird, Molothrus ater
A brood parasite:
The female, but not
the male, requires
knowledge of nest
sites
Sherry, DF. (2006) Annual Review of Psychology Vol 57 pp 167-97
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Dr Alice Witney
•
© 2008 Discovery Communications, LLC.
Hippocampal Volume: Comparison of the
brown-headed cowbird with non-brood
parasites
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Dr Alice Witney
Hippocampal Volume in Taxi Drivers
Taxi drivers show a
decrease in size of
anterior hippocampus
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Dr Alice Witney
Maguire et al (2000) PNAS Vol 97 No 8 pp 4398-4403
Taxi drivers show an
increase in size of
posterior
hippocampus
Time as a taxi driver and hippocampal volume
Changes in size of posterior
and anterior hippocampal
volume related to time as a
taxi driver
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Dr Alice Witney
A primate special skill: the hand and object
manipulation
Non-human primates
• Evolution of the
opposable thumb
enabling precision
grasping
• Development of
descending
corticospinal tract
• Cutaneous
afferents
Napier, 1970
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Dr Alice Witney
(a) tree-shrew (contrast) (b) chimpanzee
(c,h) hand, foot,a potto
(d,i) hand,foot, a tarsier.
(e) hand gibbon
(f) hand macaque
(g,j) foot, gorrilla baboon
Witney et al (2004)
TINS Vol 27 (10)
pp637-643
Efference copy
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Dr Alice Witney
Collective Behaviour
Final larval instar
solitarious and
gregarious locusts
What triggers locusts to swarm?
M. L. Anstey et al., Science 323, 627 -630 (2009)
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Dr Alice Witney
Published by AAAS
Serotonin in the thoracic CNS is
correlated with the degree of
behavioral gregarization
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Dr Alice Witney
Serotonin is necessary
M. L. Anstey et al., Science 323, 627 -630 (2009)
Published by AAAS
Neurobiology of Navigation in
Migratory animals?
• Migratory animals capable of
navigating for long distances in
unfamiliar territory
• A magnetic compass?
• The underlying neurobiology of long
distance migratory behaviour is not
well understood.
• Where might the primary sensory
receptor be? What might the receptor
be like?
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Dr Alice Witney
Bingman and Cheng (2005) Ethology, Ecology & Evolution Vol 17 pp 295-318
Neurobiology of Behaviour
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An animals response to the environment will be influenced by their
underlying nervous system
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Behaviour ultimately can be explained from the cellular properties of and
synaptic interactions among sensory neurons, interneurons and
motoneurons.
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Simpler nervous systems (Model systems) are often used to understand
how nervous systems evolve to the specific demands of the animal‟s
environment.
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With a Model Systems approach there is the aim of identifying cellular
properties and understanding neural circuits that are the basis for specific
behaviours.
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In humans, neuropsychological case studies have provided important
information about overall brain areas implicated in our performance of
certain tasks.
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The neurobiology for some behaviours is not well understood
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Dr Alice Witney