Lecture 8 Recording Neural Ac3vity
Today: Gap junc3on overview Synap3c integra3on Intracellular (single unit recordings) Voltage Clamp Current Clamp Extracellular (mul3 unit recordings) Mul3- unit recordings Local Field Poten3als (EEG, or ECoG)
Gap Junc3ons
Gap Junc3ons C j R j C j
Gap Junc3ons R j C j C j
Gap Junc3ons R j C j = ca j C m m = ca m C j C j A m >10 4 * A j C m >> C j
Gap Junc3ons R j C j = ca j C m m = ca m A m >10 4 * A j C m >> C j
Gap junctions have low-pass filtering characterstics Spikes are more attenuated than bursts spikelets burstlet 2 mv 50 mv 50 ms Burst firing
Measuring Neuronal Ac3vity Intracellular (single unit)
Measuring Neuronal Ac3vity Intracellular (single unit) Local field poten3als EEG ECoG
Measuring Neuronal Ac3vity Intracellular (single unit) Local field poten3als EEG Extracellular (mul3 unit) ECoG
Intracellular electrodes Diameter ~1 micron
Intracellular electrodes
Intracellular recording techinques Voltage Clamp (voltage source) Voltage is specified by user Current required to maintain that voltage is measured (equal and opposite to 3me- dependent ionic currents) Current Clamp (current source) Current is specified by user Voltage required to maintain that current is measured Measures changes in the membrane poten3al At I=0 records approximately the true Vm
Func3onal Proper3es of Op- Amps Property 1: If an op amp has sufficiently high gain A, then with the op- amp is operated in its linear region, v p v n Property 2: If the op amp has a very high input resistance, then ideally the input stage of the op amp draws no current These two proper3es generally simplify amplifier design using op amps as major components i p = i n 0 V Sat e o A v n v p i n i p + e0 = A(v p v n ) vp v n V Sat Input- Output Rela3onship of OP- Amp
Ideal Voltage Clamp Circuit
Ideal Current Clamp Circuit
Patch clamp configura3ons
Good and Bad Seals
Why is the seal important?
Why is the seal important?
Why is the seal important?
Why is the seal important?
Why is the seal important?
Measuring Neuronal Ac3vity Intracellular (single unit) Local field poten3als EEG Extracellular (mul3 unit) ECoG
Extracellular Recording V m
Extracellular Recording I ΔV m
Extracellular Recording j I / A = current density I = j ˆr r 2 sinθ dθdφ Spherical symmetry j = I 4πr 2 ˆr r I ΔV m
Extracellular Recording j I / A = current density I = j ˆr r 2 sinθ dθdφ Ohms Law j = σ E Spherical symmetry j = I 4πr 2 ˆr r I ΔV m Defini3on of Voltage r V E ds = V = V = r I 4πσ r 2 dr' I 4πσ r r j(r') σ dr'
Sodium dominated Potassium
Sodium dominated Potassium
Waveform depends on electrode position Gold C et al. J Neurophysiol 2006;95:3113-3128 2006 by American Physiological Society
Waveform depends on electrode position Gold C et al. J Neurophysiol 2006;95:3113-3128 2006 by American Physiological Society
Note: Unlike intracellular recordings, here individual EPSPs cannot be recorded
Far from the cell, only Local Field Poten3als (LFPs) are measured EEG ECoG
Far away: average ac3vity
EEG correlates with PSPs Simultaneous Intracellular and EEG Intracellular (AC) Strong S3mulus EEG Intracellular (DC)
EEG correlates with PSPs Simultaneous Intracellular and EEG Intracellular (AC) Weak S3mulus EEG Intracellular (DC)
EEG correlates with PSPs Simultaneous Intracellular and EEG Intracellular (AC) EEG Intracellular (DC)
What what happened to the spikes? Inhomogeneous conduc3vity leads to high pass filtering in neural 3ssue
In Vivo Measurement of Cor8cal Impedance Spectrum in Monkeys: Implica8ons for Signal Propaga8on Nikos K. Logothe3s, Christoph Kayser, Axel Oeltermann Neuron Volume 55, Issue 5 2007 809-823 hip://dx.doi.org/10.1016/j.neuron.2007.07.027 Grey maier is homogeneous and no strong frequency response
Non- point- neuron models show low- pass filtering at long distances
Debate over LFP localiza3on December 2009 LFP signal originates within 250 microns of electrode December 2011 LFP signal integrates ac3vity over cen3meters
LFP Consensus LFP dominated by ensemble averaged PSPs Integrated over some area 100s microns - cms Individual spikes (or PSPs) cannot be measured
Today: 3 measurement regimes: Intracellular Ac3on poten3als and PSPs in individual cells Extracellular (nearby) Ac3on poten3als from many cells (dis3nguishable) Extracellular (far away) Averaged ac3vity of many thousands of cells (mostly PSPs)
So Far: Ionic concentra3on differences inside and outside the cell lead to membrane poten3als Voltage gated ion channels enable these cells to generate rapid voltage signals Chemical and electrical synapses enable cells to communicate to one another Micro electrodes can measure the spiking ac3vity of individual cells and cell assemblies in vivo Next: How do we process these measured signals?