In contrast to most imaging of calcium indicators, recording neuronal activity using electrodes provides spike-time temporal resolution but low cellular yield (state of the art simultaneously recorded neurons using Neuropixels probes is ~3000 neurons using 8 probes, each of which contains 384 recording sites, yielding roughly one unit per recording site 8, 9. fMRI or PET) typically give poor spatial and temporal resolution, state of the art optical methods for imaging of genetically-encoded calcium indicators have yielded cellular spatial resolution while recording all neurons in a larval zebrafish brain (on the order of ~10 5 neurons) simultaneously at low temporal resolution (~0.5 Hz) 4, 5, although faster dynamics are possible with optical methods, including with genetically-encoded voltage indicators or lightsheet microscopy 6, 7. While established methods for whole-brain monitoring (e.g.
Ideal methods would allow us to record from all neurons in a brain (10 8 in a rat or zebra finch 1 at cellular spatial resolution and a temporal resolution on which neurons operate (kHz range) in behaving animals 2, 3. In order to understand information processing in the brain, scientists must be able to take reliable measurements from the central nervous system (CNS). High-channel-count CFEAs may thus be an alternative to traditional microwire-based electrodes and a practical tool for exploring the neural code. We include designs for interfacing the system with micro-drives or flex-PCB cables for recording from multiple brain regions, as well as a facilitated method for coating CFs with the insulator Parylene-C. Here we report the design of an expanded-channel-count carbon fiber electrode array (CFEA) as well as a method for fast preparation of the recording sites using acid etching and electroplating with PEDOT-TFB, and demonstrate the ability of the 64-channel CFEA to record from rat visual cortex. Carbon fiber (CF) electrodes are thinner and more flexible than typical metal or silicon electrodes, but the arrays described in previous reports had low channel counts and required time-consuming manual assembly.
One solution to this invasiveness problem may be probes that are small enough to fly under the immune system's radar. While electrodes allow for recording in freely-behaving animals, they tend to be bulky and stiff, causing damage to the tissue they are implanted in. However, monitoring neuronal activity over long periods of time is technically challenging, and limited, in part, by the invasive nature of recording tools. A chief goal in neuroscience is to understand how neuronal activity relates to behavior, perception, and cognition.
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