Upload
lainey
View
36
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Principles of Neural Organization Lecture 2. KEYWORDS from Lecture 1. Electrode, Microelectrode, Micron (1/1000th mm), membrane, nucleus, cytoplasm, Neuron, axon, dendrite, Schwann cell/glial cell, myelin sheath, node of Ranvier, Synapse, synaptic cleft, vesicle, neurotransmitter, - PowerPoint PPT Presentation
Citation preview
Principles of Neural Organization
Lecture 2
Electrode, Microelectrode, Micron (1/1000th mm),membrane, nucleus, cytoplasm, Neuron, axon, dendrite, Schwann cell/glial cell, myelin sheath, node of Ranvier, Synapse, synaptic cleft, vesicle, neurotransmitter,receptors, ions, permeability, ion channels, voltage-dependent sodium channels, neural threshold, positive feedback, sodium (Na+), potassium (K+), sodium-potassium pump, electrochemical equilibrium potentials, sodium (Na+) +55mv, potassium (K+) -75mv, resting potential -70mv, polarization/ depolarization/ hyperpolarization, inhibitory post-synaptic potential (IPSP), Excitatory post-synaptic potential (EPSP),integration, axon hillock, action potential (AP), all-or-none, neuron threshold -55mv, saltatory propagation, AP propagation
KEYWORDS from Lecture 1
1 -- electrical stimulation (artificial depolarization)
2 -- spatial and temporal integration of EPSPs and IPSPs across the neurone’s
membrane resulting in the neuronal threshold being reached.• Generator potential
3 -- sensory stimulation (transduction)• mechanical (cytoskeleton)• chemical (receptors, second messengers)• light (hyperpolarization)
WHEN DO CELLS PRODUCE ACTION POTENTIALS?
• MODALITY• labelled lines• specific nerve energies
• INTENSITY• proportional to frequency• population (recruitment)
• DURATION• rapidly adapting (RA)• slowly adapting (SA)
• LOCATION• locate a site• distinguish two sites• mapping
Principles of Neural Coding
Johannes Műller 1826
DOCTRINE OF SPECIFIC NERVE ENERGIES
“regardless of how a receptor is stimulated it produces only one kind of sensory experience”
MODALITY
“vision”
“hearing”
“touch”
“labeled lines”
Intensity of stimulus
Res
po
nse
of
cell
threshold
INTENSITY
recruitment of additional cells with higher thresholds
DURATION
Introduction to structure of central nervous system...
Cortex
BRAIN STEM
PARIETALFRONTAL
INFEROTEMPORAL
CEREBELLUM
Somatosensory Cortex
Motor Cortex
Common structure of the senses
•Receptive fields•sense organ -> cortex via THALAMUS•heirarchy and parallel systems•topographic arrangement
OF A SINGLE PHOTORECEPTORTHE VISUAL RECEPTIVE FIELD
a single rod
The Visual Receptive Fieldof a single photoreceptor.Light outside this regionwill have no effect on thiscell.
screen
(A) Across-fibre pattern coding
One pattern codes one thing (eg. red)....
.. and another pattern codes something else (eg. blue).
(C) Specificity coding
One cell codes one thing (eg. red)....
.. and another cell codes something else (eg. blue).
Attribute coded by relative firing
(D) Channel coding
Attribute distributionof activity
(B) Population coding
Across pattern coding• can code more than one thing at the same time• can code ‘similarity’• 2 stimuli coded as two stimuli (if sufficiently different)• Good for coding patternsPopulation coding• only codes one thing• 2 stimuli --> smaller ignored • integration of activity means all neurones involved• Good for coding a single parameter such as directionSpecificity coding• can code more than one thing• 2 stimuli always coded as separate• each neurone acts alone (therefore vulnerable)• Good for coding patternsChannel coding• only codes one thing• 2 stimuli perceived as 1 (different from either alone - metamer)• Good for extracting a single parameter in the presence of
other potentially confusing factors.
SUMMARY
Properties of neurones, action potentials, synapses
Transduction in sensory cells
Coding of modality, intensity, duration, location
Overview of structure of the brain and some of its maps
Common structure of the different senses
Coding mechanisms within the senses
Psychophysics
section 2
DETECTION THRESHOLDS
Section 1 method of limitsmethod of constant stimulimethod of adjustment
Section 2 signal detection theory
DISCRIMINATION THRESHOLDS
Section 3 Weber’s LawFechner’s LawSteven’s Power Law
PSYCHOPHYSICS
Precisionhigh
Precisionlow
Accuracyhigh
Accuracylow
bias
bias
Method of limitsbias of expectationbias of habituationstaircase
Method of constant stimuli2AFC; 4AFC
Method of adjustmentrather variable“quick and dirty”
Figure 1.12 The results of an experiment to determine the threshold using the method of limits. The dashed lines indicate the crossover point for each sequence of stimuli. The threshold - the average of the crossover values - is 98.5 in this experiment.
METHODOF
LIMITS
Figure 1.13 Results of a hypothetical experiment in which the threshold for seeing a light is measured by the method of constant stimuli. The threshold - the intensity at which the light is seen on half of its presentations - is 180 in this experiment.
METHODOF
CONSTANTSTIMULI
SIGNAL DETECTION THEORY
• response bias• sensory noise• criterion• outcome matrix (hit/miss/false alarm/correct rejection)• receiver operating characteristic curves (ROC)• sensitivity (d’ or d prime)
RESPONSE
STIMULUS
“present” “absent”
present
absent
CORRECT
CORRECT
MISS
FALSEALARM
100%
100%
percentage of false alarms
per
cen
tag
e o
f h
its
more liberal
more conservative
Figure 1.14 The difference threshold (DL). (a) The person can detect the difference between a 100-gram standard weight and a 102-gram weight but cannot detect a smaller difference, so the DL is 2 grams. With a 200-gram standard weight, the comparison weight must be 204 grams before the person can detect the difference, so the DL is 4 grams. The Weber fraction, which is the ratio of DL to the weight of the standard is constant.
DIFFERENCETHRESHOLDS
The difference threshold
• just noticeable difference (jnd)• Weber’s law (1834)
the just noticeable increment is a constant fraction of the stimulus
Weber FractionsTaste 0.08 8%
Brightness 0.08 8% Loudness 0.05 5% Vibration 0.04 4% Line length 0.03 3% Heaviness 0.02 2% Electric shock 0.01 1%
• Fechner’s law (1860)sensation magnitude proportional to
logarithm (stimulus intensity)assumption: all jnd’s are the samestood for 100 years!
• Steven’s law (1961)(“To honour Fechner and repeal his law”)
sensation magnitude proportional to (stimulus intensity) raised to a power
Consequences of Steven’s Law
• response compression• response expansion• linear on a log scale
Response compression
Response expansion