Neurobiology II – BIO 354 - Formalitiesraghav/pdfs/neurobiology2/... · BIO 354 - Neurobiology 2...

BIO 354 - Neurobiology 2 1

Neurobiology II – BIO 354 - Formalities

● Course co-ordinators

– Dr. Suhita Nadkarni * (second half of the course)

– Raghav (first half of the course)

● Course website

– http://www.iiserpune.ac.in/~raghav/bio354.html

– Lectures (not enough!)

● Course textbooks (read!!)

– Principles of neural science – Eric Kandel, James Schwartz and Thomas Jessell (4th edition)

– Papers from journals (will be announced in class/website)

http://www.iiserpune.ac.in/~raghav/bio354.html


Neurobiology II – BIO 354 – Formalities (contd...)

● Assessment

– Endsem and midsem exams – 25% each

– Quizzes, assignments, etc. - 50% (25% before midsem and 25% after)

– Before midsem● 2-3 components

● Attendance

– Important along with active participation

● No fixed office hours for the course. Email me for appointments/doubts regarding my part of the course

([email protected])

mailto:[email protected]


'The Astonishing Hypothesis' – by Francis Crick

The Astonishing Hypothesis is that "You," your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will, are in fact no more than the behavior of a vast assembly of nerve cells and their associated molecules.

As Lewis Carroll's Alice might have phrased: "You're nothing but a pack of neurons."


Course syllablus

● Sensory systems

– Introduction

– Vision

– Audition

– Chemosensation

– Somatosensation

● Sleep and circadian rhythms

● Autonomic nervous system

● Motor control, pattern generators

● Processing of emotion

● Learning and memory

● Neurobiology of perception and cognition


Lecture 1 – Introduction to sensory systems

Raghav RajanBio 354 – Neurobiology 2

January 07th 2015


What is the basic function of brain?

● Sense the external (and internal) environment

● Based on the situation, nervous system needs to make a decision on what to do

– Assessment of relevant environmental conditions

– Use past experience also for deciding on the course of action (learning, memory)

● Act on that decision and produce the correct movement

● Continuous process (except maybe during sleep) – may not be discrete processes


http://www.schoppiklab.com/pubs-data/jneuro06


How does the brain do this? (Review of Neurobiology 1)

● Neurons

● Action potentials

● Synapses

http://en.wikipedia.org/wiki/Neuron#mediaviewer/File:Purkinje_cell_by_Cajal.png

http://en.wikipedia.org/wiki/Action_potential#mediaviewer/File:Action_potential.svg

http://en.wikipedia.org/wiki/Synapse#mediaviewer/File:Synapse_Illustration_unlabeled.svgvg


How does the brain sense the external environment?

● The outside world (stimulus)

● This stimulus has to be transduced into spikes

● Spikes then have to be interpreted and converted back into a picture of the outside world

– Spikes give rise to a percept

● Two different fields of study

– Psychophysics

– Sensory physiology

● In other words, the brain BUILDS a picture of the external world

● Constrained by the architecture and functioning of networks of neurons


General principles of sensory systems

● Weber and Fechner – sensory psychophysics

● 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)


What is the stimulus – Sensory modality

● Labeled line code

http://courses.evanbradley.net/wiki/lib/exe/detail.php?id=overview_of_sensory_systems&media=sensory_systems.jpg




● Different specialized receptors for different stimuli

● Response specificity of receptors – important for labeled line code

● Receptors respond to different types of energy

– light, chemicals, pressure, etc.

– Transduction process also different

http://www.ib.cnea.gov.ar/~redneu/2013/BOOKS/Principles%20of%20Neural%20Science%20-%20Kandel/gateway.ut.ovid.com/gw2/ovidweb.cgisidnjhkoalgmeho00dbookimagebookdb_7c_2fc~27.htm




● Different specialized receptors for different stimuli

● Response specificity of receptors – important for labeled line code

● Receptors respond to different types of energy

– light, chemicals, pressure, etc.

– Transduction process also different

● Receptors have tuning curves (caveats?)



Where is the stimulus - location

● Spatial distribution of sensory receptors

● Receptive field of a sensory neuron

● Spatial resolution capabilities

● Regions of higher resolution – fovea, finger tips



How strong is the stimulus - Intensity

● Amplitude of stimulus related to intensity of sensation

● Usefulness of determining stimulus intensity

– Discriminating between same stimulus (modality) but different strength

– Evaluating stimulus amplitude

● Weber, Fechner, Helmholz and von Frey (first psychophysicists) quantified intensity of sensation and developed expressions for stimulus magnitude and sensory discrimination

● The field of psychophysics – understanding the relationship between the physical properties of the stimulus and attributes of sensory experience


Weber's law

● Subjects were blindfolded

● Put a weight on the person's hand

● Weber would slowly add more weights

● And asked when the person noticed that the weight had increased

● ΔS/S = K – Weber's law (just noticeable difference)


How strong is the stimulus - Intensity

● Amplitude of stimulus related to intensity of sensation

● Usefulness of determining stimulus intensity

– Discriminating between same stimulus (modality) but different strength

– Evaluating stimulus amplitude

● Weber, Fechner, Helmholz and von Frey

● ΔS = K X S – Weber's law (just noticeable difference)

● I = K log S/So – Fechner extension (intensity of stimulation/ response follows a logarithmic relationship)

● I = K(S – So)n – Stanley Stevens (power law)

● Sensory threshold


Psychometric curves to evaluate sensory thresholds

● Absolute detectability of stimulus

● The criterion set by the subject to determine if a stimulus is present (False +ves and false -ves)


Firing rates of neurons can encode stimulus magnitude



Firing rates, patterns also represent timing of stimulus

● Also constrained by properties of the receptor

● Another important principle – adaptation

● Increase in dynamic range

● Detecting changes



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

Neurobiology II – BIO 354 - Formalitiesraghav/pdfs/neurobiology2/... · BIO 354 - Neurobiology 2...

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