[mattkrause]

To elaborate a little bit more, brain activity can be measured non-invasively with things like EEG, MEG, fMRI, or fNIRS. However, these only let you look at the average activity of fairly large groups of neurons. EEG and MEG directly measures the neurons’ activity, and so have excellent temporal resolution, but their spatial specificity is pretty bad: EEG detects the electrical activity directly, but it’s smeared out by the skull and scalp; MEG avoids this by measuring magnetic fields, but can only sense them when they’re in certain orientations relative to the detectors, which limits where you can record on a curved, wrinkly brain. fMRI and fNIRS don’t sense the activity directly, but instead measure changes in blood flow/oxygenation that are related to neural activity. This is slower (by seconds) but has good spatial resolution. Thus, there’s not really an alternative for these invasive recordings...