electrophysiology of neurons. some things to remember…
TRANSCRIPT
Electrophysiology of neurons
Some things to remember…
Electrical properties of a (simplified) single cell
Differences in ion concentrations set up by Na+-K+ ATPase pump – high [K+], low [Na+, Cl-] inside cell; high [Na+, Cl-] , low [K+] outside cell
Voltage-gated ion channels alter permeability to Na+ and K+ during generation of action potential
Permeability of membrane to these ions determines the membrane potential
Ligand-gated ion chanels alter permeability to Na+,K+ , Cl- during generation of synaptic potentials
Electrical properties of a (simplified) single cell
ALL or NOTHING: binary, point process
SUMMED input from (tens of) thousands of synapses: continuous process
40ms
20pA
synaptic potentials
action potentials
Cells differ from one another – morphologically
Scale bar = 100 microns Segev, 1998
Cells differ from one another – electrically
There are lots of them
Buzsaki, 2004(≈ 5-10 million cells in a 3x3x3mm voxel)
What do we want to know about?To investigate… We use…
Membrane properties, properties of synapses
Intracellular recording: sharp microelectrodes or patch electrodes (but also calcium imaging)
Single cells, firing patterns in response to environmental stimuli, labelled cells
Extracellular recording
Multiple cells, firing patterns in response to each other, distribution of responses
Tetrode/silicon probe recording (but also population imaging)
Populations of cells acting in synchrony, synaptic input to a population
Local field potential recording
Intracellular recording
Aims to establish something about the properties of single cell, e.g. membrane properties or properties of synapse
Needs an electrode whose tip is smaller than the cell! (typically 50-500 nm)
a lot of mechanical stability
Classic example – miniature synaptic potentials
Fatt & Katz, 1952
Patch clamping
after Neher & Sakmann, 1970s
State of the art – in vivo patch clamp
Bruno & Sakmann, 2006
Intracellular recording: pros and cons
permits measurement of synapses/membrane properties
we can fill the cell with a dye (and reconstruct it afterwards)
difficult to obtain in vivo recordings (normally anaesthetised)
cell damage affects physiology
Sjostrom and Hausser, UCL(also state of the art!)
Extracellular recording
Aims to record firing patterns of a cell, typically with respect to environment/behaviour
Needs electrode that will remain stable during recording – less stringent than intracellular so in vivo recording more straightforward
May need spike sorting to differentiate cells recorded on same electrode
Classic example – visual cortex
Hubel & Wiesel, 1960s
State of the art – juxtacellular recording
after Pinault et al., 1996
State of the art – juxtacellular recording
Ungless et al., 2004
Extracellular recording – pros and cons
can use in awake, behaving animals
difficult to know which cell you’re recording (juxtacellular technique has low yield)
may bias sampling when listening for ‘noisy’ cells/cells with certain response property
spike variability assumed to be noise, when it might not be…
Multi-unit recording
Aims to record activity of populations of cells stimultaneously
Needs some clever maths and technology to pick out the individual voices in the chorus
Tetrodes
Buzsaki, 2004
Silicon probes
Buzsaki, 2004
Example – spike cross-correlograms
Fujisawa et al., 2008
Two-photon calcium imaging
Ohki et al., 2006
Multi-unit recording – pros and cons
can begin to ask sophisticated questions about populations carrying meaningful information (acting as ‘cell assemblies’)
can examine the interactions between cells and how these change during task
can never label cells (although can identify putative interneurons/excitatory cells)
limited by how well we can separate units from one another
Local field potential
Aims to record gross current flow in extracellular space
Reflects synaptic inputs into dendritic trees with particular orientations – so low frequency cf. action potentials (typically lowpass filter at 300Hz)
LFP and cortical depth
Current source density analysis
Mitzdorf, 1985
Relationship between LFPs and EEG: confusing!
Mitzdorf, 1985
Phase-locking between LFP oscillations and spike timing of different cells
Klausberger et al., 2008
What do we want to know about?To investigate… We use…
Membrane properties, properties of synapses
Intracellular recording: sharp microelectrodes or patch electrodes (but also calcium imaging)
Single cells, firing patterns in response to environmental stimuli, labelled cells
Extracellular recording
Multiple cells, firing patterns in response to each other, distribution of responses
Tetrode/silicon probe recording (but also population imaging)
Populations of cells acting in synchrony, synaptic input to a population
Local field potential recording
Relating neural activity to BOLD fMRI signals
Red = BOLD fMRI timecourseBlue = LFPGreen = single unit spiking Logothetis, 2001