NeuroScience Neuroelectronic Interfacing: Semiconductor Chips with - PowerPoint PPT Presentation

Nanoelectronics and Nanotechnology NeuroScience Neuroelectronic Interfacing: Semiconductor Chips with Ion Channels, Nerve Cells and Brain João Abrantes nº 65693 Teresa Jorge nº 65722 Tomás Cruz nº 65725

NeuroScience State of the art Electrodes stimulation Brain Imaging and PET Scan Nanoelectronics and Nanotechnology – 1st 2 Semester 2011/2012 – MEFT

NeuroScience State of the art Zebrafish brain Optogenetics Nanoelectronics and Nanotechnology – 1st 3 Semester 2011/2012 – MEFT

Neurons Nanoelectronics and Nanotechnology – 1st 4 Semester 2011/2012 – MEFT

NeuroScience Neuron Anatomy Synapse Nucleous Body cell Dendrite Soma Axon Axon Terminal Nanoelectronics and Nanotechnology – 1st 5 Semester 2011/2012 – MEFT

NeuroScience Different Neurons Nanoelectronics and Nanotechnology – 1st 6 Semester 2011/2012 – MEFT

NeuroScience Synapse  Transfer of information between neurons  Axon terminal.  Synaptic vesicles.  Neurotransmitters-biochemical agents.  Synaptic cleft  Receptors  Dendrits Nanoelectronics and Nanotechnology – 7 1st Semester 2011/2012 – MEFT

NeuroScience Ion concentration Lipid membrane separating interior  from exterior medium. Different concentration of Na + and K +  ions inside and outside of the cell. Higher concentration of K + inside  Higher concentration of Na + outside  Nanoelectronics and Nanotechnology – 1st 8 Semester 2011/2012 – MEFT

NeuroScience Diffusion potential Diffusion occurs in the direction of the concentration gradient.  K + inside out  Na + outside in  Membrane100x more permeable to K + ions than to Na + ions  Voltage stops flow  Rest voltage ~-90mv. Nanoelectronics and Nanotechnology – 1st 9 Semester 2011/2012 – MEFT

NeuroScience K + and Na + Pumps To make the ions pass through the membrane against the concentration gradient the neuron has K + and Na + Pumps. This transport requires energy to happen. And happens at different rates for K + and Na +. Nanoelectronics and Nanotechnology – 1st 10 Semester 2011/2012 – MEFT

NeuroScience Action potential  Transfer of information through the neuron Electrical signal  Propagates near the cell membrane.  Rest potential at -90mv   3 phases Rest Despolarization Repolarization How does it work? Nanoelectronics and Nanotechnology – 1st 11 Semester 2011/2012 – MEFT

NeuroScience Action potential Depolarization Membrane gets permeable to Na + , it enters the cell and increases voltage. Repolarization Membrane closes Na + channels and opens K + channel. Na + stops flowing in, K + flows out. Voltage decreases. Trigger is voltage. Nanoelectronics and Nanotechnology – 1st 12 Semester 2011/2012 – MEFT

NeuroScience Action potential Depolarization Membrane gets permeable to Na + , it enters the cell and increases voltage. Repolarization Membrane closes Na + channels and opens K + channel. Na + stops flowing in, K + flows out. Voltage decreases. Trigger is voltage. Nanoelectronics and Nanotechnology – 1st 13 Semester 2011/2012 – MEFT

NeuroScience Action potential Beginning of action potential When the voltage rises a little above -90mv the action potential begins. Feedback The rising of the voltages opens the Na + channels. The opening of the channels allows the voltage to rise faster. It is a feedback process. For the feedback process to suffice, the All or nothing Principle voltage should in the first impulse rise above When there are conditions for the potential a certain voltage. to propagate, it propagates. When there are not, it doesn't. There isn't half potentials. Nanoelectronics and Nanotechnology – 1st 14 Semester 2011/2012 – MEFT

NeuroScience Action potential Propagation of action potential The potential propagates to the neighbor membrane, in both directions. Nanoelectronics and Nanotechnology – 1st 15 Semester 2011/2012 – MEFT

Interface Model Nanoelectronics and Nanotechnology – 1st 16 Semester 2011/2012 – MEFT

NeuroScience Micro/Nanoelectronic Devices Neurons Hundreds of nanometers Micrometers Electrical signals Electrical signals Nanoelectronics and Nanotechnology – 1st 17 Semester 2011/2012 – MEFT

NeuroScience À priori possible problems: • Charge carriers are different and their mobility is very different! Electrons in the electronic device and Ions in the neurons. • Different architecture of the two information processors. Conclusion: Direct communication between single neuron and nanoelectronic device should be no big deal! Nanoelectronics and Nanotechnology – 1st 18 Semester 2011/2012 – MEFT

NeuroScience Model of interface, what do we know already: • Neuron is surrounded by a lipid membrane that is a insulating material. • Neuron membrane has proteins responsible for ionic currents trough the membrane. • Standard nanoelectronics, insulating layer over a substratum. Nanoelectronics and Nanotechnology – 1st 19 Semester 2011/2012 – MEFT

NeuroScience Most simple model, global contact. Membrane and insulator layer forms a compact dielectric: • Easy to polarize and be polarized by the neuron. (A variable voltage in the neuron directly polarizes the substratum and a variable voltage in the neuron) This model doesn’t work , reality is just not that simple! Nanoelectronics and Nanotechnology – 1st 20 Semester 2011/2012 – MEFT

NeuroScience So, why does it not work? Big proteins and irregularities in the membrane don’t allow global contact. There is no compact dielectric. Nanoelectronics and Nanotechnology – 1st 21 Semester 2011/2012 – MEFT

NeuroScience More realistic interface model: core coat conductor . A conductive cleft is created between the membrane and the insulator layer. The conductive cleft suppress mutual polarization and shield electric fields. Nanoelectronics and Nanotechnology – 1st 22 Semester 2011/2012 – MEFT

NeuroScience Interface • The current that flows across the cleft origins a transductive potential between the membrane and the insulator layer. • Polarization will occur but will be mediated by the transductive potential. The current that flows in the cleft will be the base of the interface will have its origin in: • Conductive current from the ion channels. • Displacement current through the membrane. • Displacement current through the insulator layer. Nanoelectronics and Nanotechnology – 1st 23 Semester 2011/2012 – MEFT

NeuroScience Next simplest model: Point contact model . Balance equation 1: Kirchhoff current law: Nanoelectronics and Nanotechnology – 1st 24 Semester 2011/2012 – MEFT

NeuroScience Balance Equation 2: Kirchhoff current law: Nanoelectronics and Nanotechnology – 1st 25 Semester 2011/2012 – MEFT

NeuroScience Neuron-Silicon Circuits Neuronal Activity Capacitive Stimulation Transistor Recording Nanoelectronics and Nanotechnology – 1st 26 Semester 2011/2012 – MEFT

Recording Nanoelectronics and Nanotechnology – 1st 27 Semester 2011/2012 – MEFT

NeuroScience Transistor Recording of Neuronal Activity • What will be the read of transistor ? Inside Neuron Membrane potential V M (t) Transductive Extracellular Potential V J (t) Cleft Nanoelectronics and Nanotechnology – 1st 28 Semester 2011/2012 – MEFT

NeuroScience Transistor Recording of Neuronal Activity • Calculation of V J (t) , according to Point-Contact Model Small Signal Aproximation Balance Equations Nanoelectronics and Nanotechnology – 1st 29 Semester 2011/2012 – MEFT

NeuroScience Transistor Recording of Neuronal Activity • Calculation of V J (t) , according to Point-Contact Model Small Signal Aproximation (small V J (t) ) V E = 0 Current injected by a pipette  V M (t) is governed by the currents through attached and free membrane.  V J (t) is determined by the capacitive and ionic current through the attached membrane. Nanoelectronics and Nanotechnology – 1st 30 Semester 2011/2012 – MEFT

NeuroScience Transistor Recording of Neuronal Activity • A-, B- and C-type response  A-type response i =0); 1. The attached membrane contains no voltage-gated conductances (V o 2. Negligible leak conductance (g JM ≈0). dV M  V J  dV M g J V J  g JM V M  c M dt dt  B-type response i =0); 1. The attached membrane contains no voltage-gated conductances (V o 2. Dominating ohmic leak conductance. ฀ dV M g J V J  g JM V M  c M  V J  V M dt  C-type response ฀ Nanoelectronics and Nanotechnology – 1st 31 Semester 2011/2012 – MEFT

NeuroScience Transistor Recording of Neuronal Activity • Experiments of Neuronal Activity Vs Why neurons of invertebrates are preferred ? • They are large and easy to handle; • They form strong neuroelectronic junctions; • Small networks may be reconstitued and studied on a chip. Nanoelectronics and Nanotechnology – 1st 32 Semester 2011/2012 – MEFT

NeuroScience Transistor Recording of Neuronal Activity • Experiments of Neuronal Activity – Leech Neuron Cell Body of a neuron Axon stump of a neuron on the open gate oxide on a linear array of of field-efect transistor. field-efect transistors. Nanoelectronics and Nanotechnology – 1st 33 Semester 2011/2012 – MEFT