Lecture 8. Recording Neural Ac3vity

Transcription

1 Lecture 8 Recording Neural Ac3vity

2 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)

3 Gap Junc3ons

4 Gap Junc3ons C j R j C j

5 Gap Junc3ons R j C j C j

6 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

7 Gap Junc3ons R j C j = ca j C m m = ca m A m >10 4 * A j C m >> C j

8 Gap junctions have low-pass filtering characterstics Spikes are more attenuated than bursts spikelets burstlet 2 mv 50 mv 50 ms Burst firing

9 Measuring Neuronal Ac3vity Intracellular (single unit)

10 Measuring Neuronal Ac3vity Intracellular (single unit) Local field poten3als EEG ECoG

11 Measuring Neuronal Ac3vity Intracellular (single unit) Local field poten3als EEG Extracellular (mul3 unit) ECoG

12 Intracellular electrodes Diameter ~1 micron

13 Intracellular electrodes

14 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

15 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

16 Ideal Voltage Clamp Circuit

17 Ideal Current Clamp Circuit

18 Patch clamp configura3ons

19 Good and Bad Seals

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21 Why is the seal important?

22 Why is the seal important?

23 Why is the seal important?

24 Why is the seal important?

25 Why is the seal important?

26 Measuring Neuronal Ac3vity Intracellular (single unit) Local field poten3als EEG Extracellular (mul3 unit) ECoG

27 Extracellular Recording V m

28 Extracellular Recording I ΔV m

29 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

30 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'

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32 Sodium dominated Potassium

33 Sodium dominated Potassium

34 Waveform depends on electrode position Gold C et al. J Neurophysiol 2006;95: by American Physiological Society

35 Waveform depends on electrode position Gold C et al. J Neurophysiol 2006;95: by American Physiological Society

36 Note: Unlike intracellular recordings, here individual EPSPs cannot be recorded

37 Far from the cell, only Local Field Poten3als (LFPs) are measured EEG ECoG

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41 Far away: average ac3vity

42 EEG correlates with PSPs Simultaneous Intracellular and EEG Intracellular (AC) Strong S3mulus EEG Intracellular (DC)

43 EEG correlates with PSPs Simultaneous Intracellular and EEG Intracellular (AC) Weak S3mulus EEG Intracellular (DC)

44 EEG correlates with PSPs Simultaneous Intracellular and EEG Intracellular (AC) EEG Intracellular (DC)

45 What what happened to the spikes? Inhomogeneous conduc3vity leads to high pass filtering in neural 3ssue

46 In Vivo Measurement of Cor8cal Impedance Spectrum in Monkeys: Implica8ons for Signal Propaga8on Nikos K. Logothe3s, Christoph Kayser, Axel Oeltermann Neuron Volume 55, Issue hip://dx.doi.org/ /j.neuron Grey maier is homogeneous and no strong frequency response

47 Non- point- neuron models show low- pass filtering at long distances

48 Debate over LFP localiza3on December 2009 LFP signal originates within 250 microns of electrode December 2011 LFP signal integrates ac3vity over cen3meters

49 LFP Consensus LFP dominated by ensemble averaged PSPs Integrated over some area 100s microns - cms Individual spikes (or PSPs) cannot be measured

50 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)

51 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?