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Lecture 14 – Sensory systems reviewHow do we really sense things?

Raghav RajanBio 354 – Neurobiology 2

February 19th 2015

All lecture material from the following links unless otherwise mentioned:1. Research papers or other links mentioned on slide

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From earlier classes ...!!

● Vishnu

BIO 354 - Neurobiology 2 3

General principles of sensory systems

● All sensory systems convey 4 basic types of information

– What is the stimulus (modality) – Different sensory systems

– Where is the stimulus (location) – Different subsets of neurons

– How strong is it (intensity) – Firing patterns (rate and timing)

– When did it come on, when did it go off (timing) – Firing patterns (rate and timing)

● The brain BUILDS a picture of the external world

● Constrained by the architecture and functioning of networks of neurons

● Understanding the basic anatomy and functioning is necessary for going further

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Studying perception

● Illusions

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Object perception - shadows

● Shadows imply a light source

● We assume there is only one light source

● Second figure perceived as bumps and depressions

http://www.ib.cnea.gov.ar/~redneu/2013/BOOKS/Principles%20of%20Neural%20Science%20-%20Kandel/gateway.ut.ovid.com/gw2/ovidweb.cgisidnjhkoalgmeho00dbookimagebookdb_7c_2fc~31.htm

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Studying perception

● Illusions

● Psychophysics

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Psychophysics

● Outer psychophysics – the relationship between physical stimulus and sensation

● Inner psychophysics – theoretical idea of the internal neuronal representation resulting in sensation – largely inferred from outer pscyhophysics

● Importantly, can be compared between humans and animals

http://www.uni-leipzig.de/~isp/isp/history/texts/PSYPHY-M.PDF

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Comparing vibration amplitude discrimination thresholds in humans and macaques

http://jn.physiology.org/content/jn/38/3/539

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Comparing vibration amplitude discrimination thresholds in humans and macaques

http://jn.physiology.org/content/jn/38/3/539

● Standard vibration – 30Hz and 102 μm amplitude

● Comparison stimuli – 30Hz and 61-143 μm amplitude

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Comparing vibration frequency discrimination thresholds in humans and macaques

http://jn.physiology.org/content/jn/38/3/539

● Standard vibration – 30Hz

● Comparison stimuli – 24 – 36 Hz

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What do we perceive, what do neurons perceive and how are the two related?

● Neurophysiology – relationship between neuronal activity and the stimulus

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Frequency discrimination of vibration stimuli (flutter – 5-50Hz) by macaque monkeys

● Monkeys learn to discriminate the frequency of two vibratory stimuli on their fingers

http://www.cns.nyu.edu/~david/courses/sm12/Readings/Romo_Salinas%20nrn2003.pdf

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Recording neuronal

activity during the task -

correlation● What aspect

of the neuron's response carries information about the stimulus

● About the behavior

● Firing rate?

● Firing pattern?

http://www.cns.nyu.edu/~david/courses/sm12/Readings/Romo_Salinas%20nrn2003.pdf

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● Caveats

Microstimulation can evoke perception of a

real stimulus

http://www.cns.nyu.edu/~david/courses/sm12/Readings/Romo_Salinas%20nrn2003.pdf

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Studying the relationship between neural activity and perception in humans – different spatiotemporal scales

● fMRI

● PET

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http://www.bobblum.com/ESSAYS/NEUROPSYCH/BAM.html

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Studying the relationship between neural activity and perception in humans - Causation

● Damage due to injury

● TMS

● Caloric vestibular stimulation

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Looking at the role of two hemispheres in binocular rivalry

http://www.uq.edu.au/nuq/jack/CBrivalry.pdf

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Labelled line vs. distributed representations – Grandmother cell debate

● Could ultimately be a combination of both

BIO 354 - Neurobiology 2 19

General principles of sensory systems

● All sensory systems convey 4 basic types of information

– What is the stimulus (modality) – Different sensory systems

– Where is the stimulus (location) – Different subsets of neurons

– How strong is it (intensity) – Firing patterns (rate and timing)

– When did it come on, when did it go off (timing) – Firing patterns (rate and timing)

● The brain BUILDS a picture of the external world

● Constrained by the architecture and functioning of networks of neurons

● Understanding the basic anatomy and functioning is necessary for going further