Exploring Sensory Coding and Electrophysiological Recordings
School
University of California, Davis**We aren't endorsed by this school
Course
CHE UNKNOWN
Subject
Psychology
Date
Dec 10, 2024
Pages
22
Uploaded by DeanSnakeMaster1939
NPB 100L:Neurobiology LaboratoryToday:0) Announcements:Look for prelab posted after class on Canvas1) Sensory Coding2) Electrophysiological recordings:▪ Characterizing sensory encoding in the cockroach
Thought question:Sensory codingSuppose you discover a new organism and wish to understandhow it processes sensory information.Where would you start? What would you try to measure or characterize?
Discovery that primary visual cortex cells respond preferentially to oriented barsCharacterizing the Responses of a Visual Cortex NeuronDavid Hubel & Torsten Wiesel (Nobel Prize, 1981)http://www.youtube.com/watch?v=8VdFf3egwfgTorsten WieselDavid Hubel
V1 neuron response to a moving bar:Tuning Curves: Neuronal Response as a Function of a Single Stimulus Dimensionorientation(deg)trial-averagedfiring rate (spikes/sec)Orientation tuning curveResponses characterized by (average across many trials of):Firing rate = (# of spikes in a given time period)/(duration of time period)Example: 30 spikes recorded over 2 seconds = 15 spikes/sec
V1 neuron response to changing the brightness (luminance) of a stimulus:Another Example: Luminance Tuning CurvesLi & Wang, Scientific Reports, 2013Firing rate (spikes/sec)
Lab 1: Neurophysiology of Sensory Perception:Mapping the Sensory Responses of Cockroaches
Recording Action Potentials (aka “Spikes”)▪ Action potentials conduct long distances, and thus are useful for conveying information across large distances▪ Spikes from a given neuron are highly stereotyped in their waveform. Thus, spike shape/amplitude typically does not convey information Rather, the timing or pattern of spikes conveys informatione.g. Train of spikes recorded intracellularly from a neocortical pyramidal neuron:Notice: ▪ We say these spikes “encode” information about stimuli. This information can then be “decoded” to estimate the stimulus.
Two Methods for RecordingExtracellular recording:Electrode outside the cell measuresvoltage near the cell relative to reference voltage far awayIntracellular recording:Electrode inside the cell measuresvoltage across the cell membrane
Two Methods for Recording1) Intracellular or “transmembrane” recordingAll spikes look alike, and are roughly the same size (~10’s mV)2) Extracellular recording▪ Very small voltages (e.g. 10’s mV) arising from currents that trickle out of cell▪ Multiple nearby neurons may be recorded▪ Extracellular spike size primarily reflects axon diameter and distance of recording electrodefrom the cell, notthe size of the intracellular action potentialintracellularrecordingextracellularrecordingvoltage scale:~10’s-100’s of mV(you’ll see this in lab!)
Periplanita Americana (“American Cockroach”)Sensory receptors (‘sensilla’) on the leg:• Tactile spines• Campaniform organs(within joints)
The Cockroach Leg
A Single Spine
Innervation of a Spinea single axon arisesfrom each spine
Thought QuestionQ: Suppose you are doing an extracellular recording of theaxon coming from a spine. As you bend the spine further, do you expect:1)You will see more action potentials generated2)The action potential you record will become larger3)Both 1 and 2.
Slides for beginning of lab on Thursday
How We’ll Make These RecordingsEquipment:Stereo microscopePin electrodesAmplifier Analog-to-digital (A-D) converterComputer (oscilloscope/strip chart recorder)electrodes recordingcockroach leg(analog, small signals)Preamplifier(analog, larger signals)Analog-to-digitalConverter(digital signals)to oscilloscope
Simultaneous Intracellular & ExtracellularRecordings of an Action PotentialNote smaller scale for extracellular(and 5 mV is unusually large; usually expect10’s – 100’s mVextracellularly)
Adaptation & Temporal Response CharacteristicsStimulus:Spiking response 1:initial response: higher firing ratelater response: lower firing rate3 possible responses to a presented stimulus:timeSpiking response 3:Spiking response 2:“tonic”“phasic”, “rapidly adapting”“phasic-tonic”offonThese are qualitative descriptions of the data
Quantitative Characterization of Responsesinitial response: higher firing ratelater response: lower firing rateQ: How can we quantitativelydescribe these data?e.g. Spiking response 3:A: Calculate the firing rate in small bins of timeFiring rate (spikes/sec)Time (ms)
Extra Slides
The Campaniform Organfemoro-tibialjointCampaniform sensilla within theseorgans detect appliedforces.They are roughly analogous to mammalian Golgi tendon organs.