Electrophysiology

Electrophysiology is the study of electrical properties of biological cells and tissues. In neuroscience, this primarily means recording voltage changes caused by ion flows across neuronal membranes.

Types of electrophysiology:

• Intracellular: Recording from inside a single cell (patch clamp, sharp electrode)
• Extracellular: Recording from tissue outside cells (most probe recordings)
• In vitro: Isolated tissue (brain slices, cultured neurons)
• In vivo: Living animals (acute or chronic)

What we measure:

• Action potentials: Brief voltage spikes (~1 ms, ~100 µV extracellular)
• Synaptic potentials: Slower voltage changes from synaptic input
• Field potentials: Population activity from many neurons
• Brain rhythms: Coordinated oscillations across neural networks

Extracellular vs intracellular: Extracellular recordings (what probes do) measure voltage in tissue fluid outside neurons. This detects action potentials but not subthreshold activity. Intracellular recording measures voltage inside cells, capturing all electrical events but only from one neuron at a time.

Why silicon probes revolutionized electrophysiology: Multiple recording sites allow simultaneous sampling of many neurons, revealing population dynamics and coordination that single-electrode recordings cannot show.