(he/him)
Home Department: Physics (Machta & Lynn Labs)
Research Project (Machta Lab): How the physics of noise determines the sensitivity of ion channels
Voltage-gated ion channels are essential for propagating signals in neurons. Each channel senses the local membrane potential created by nearby ions. Fluctuations in these ions introduce two fundamental noise sources: (i) shot noise, from the discreteness of ionic charge, and (ii) Johnson–Nyquist noise, from slow thermal fluctuations of the charge accumulated at the membrane. We show that, for an individual channel, shot noise dominates and sets an intrinsic limit to voltage sensing. On the ~10 μs timescales relevant to channel gating, this limit corresponds to an accuracy of about ~10 mV - close to measured channel sensitivities. When signals from many channels are aggregated, Johnson–Nyquist noise eventually overtakes shot noise and bounds the total information that can be sensed from the environment. These results provide design principles for single‑channel architecture and collective sensing, and suggest that neuronal computation is ultimately constrained by thermal fluctuations.
Relevant Publications
Bryant and Machta (2023) Physical Constraints in Intracellular Signaling: The Cost of Sending a Bit
The ion channel senses charge in a region of linear size σO. Charge is screened for lengths larger than the Debye length lD, such that charge accumulation can only happen within lD of the membrane.
Saturation of the signal-to-noise ratio from an integrated signal as the number of ion channels increases. Shot noise dominates for small N, while Johnson-Nyquist noise dominates once the signal saturates.