Moreover, the monkey EEG bridged the gap between direct and indirect recordings. The brain of the human participants was monitored using MEG in the monkeys, EEG provided an indirect measure of brain activity, while microelectrodes directly revealed the activity of thousands of individual neurons.Īll three recordings contained information about movement and color. ![]() had monkeys and healthy human volunteers perform the same task, where they had to watch a series of colored dots moving across a screen. Yet, it is difficult to know how activity measured inside the brain relates to that measured outside. In animals, and in patients undergoing brain surgery, scientists can use hair-thin microelectrodes to directly record the activity of individual neurons. However, the brain consists of billions of neurons interconnected to form complex circuits, and EEG or MEG cannot reveal changes in activity of these networks in fine detail. Both EEG and MEG only require a few dozen sensors, placed centimeters away from the brain itself, but they can reveal the precise timing and rough location of changes in neural activity. Electrical activity within the brain also generates a weak magnetic field above the scalp, which can be measured using a technique known as MEG. Neurons carry information in the form of electrical signals, which we can listen to by applying sensors to the scalp: the resulting recordings are called an EEG. We show how information-based methods and monkey EEG can identify analogous properties of visual processing in signals spanning spatial scales from single units to MEG – a valuable framework for relating human and animal studies. Source level analysis revealed corresponding information and latency gradients across cortex. Thus, MEG and EEG were dominated by early visual and ventral stream sources. Tuning of the non-invasive signals was similar to V4 and IT, but not to dorsal and frontal areas. Motion direction and color information were accessible in all signals. Furthermore, we performed simultaneous microelectrode recordings from 6 areas of macaque cortex and human MEG. To close this gap between invasive and non-invasive electrophysiology we developed and recorded human-comparable EEG in macaque monkeys during visual stimulation with colored dynamic random dot patterns. ![]() It remains challenging to relate EEG and MEG to underlying circuit processes and comparable experiments on both spatial scales are rare.
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