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We describe a method to conduct single-neuron recordings with simultaneous eye tracking in humans. We demonstrate the utility of this method and illustrate how we used this approach to obtain neurons in the human medial temporal lobe that encode targets of a visual search.
Intracranial recordings from patients with intractable epilepsy provide a unique opportunity to study the activity of individual human neurons during active behavior. An important tool for quantifying behavior is eye tracking, which is an indispensable tool for studying visual attention. However, eye tracking is challenging to use concurrently with invasive electrophysiology and this approach has consequently been little used. Here, we present a proven experimental protocol to conduct single-neuron recordings with simultaneous eye tracking in humans. We describe how the systems are connected and the optimal settings to record neurons and eye movements. To illustrate the utility of this method, we summarize results that were made possible by this setup. This data shows how using eye tracking in a memory-guided visual search task allowed us to describe a new class of neurons called target neurons, whose response was reflective of top-down attention to the current search target. Lastly, we discuss the significance and solutions to potential problems of this setup. Together, our protocol and results suggest that single-neuron recordings with simultaneous eye tracking in humans are an effective method to study human brain function. It provides a key missing link between animal neurophysiology and human cognitive neuroscience.
Human single-neuron recordings are a unique and powerful tool to explore the function of the human brain with extraordinary spatial and temporal resolution1. Recently, single-neuron recordings have gained wide use in the field of cognitive neuroscience because they permit the direct investigation of cognitive processes central to human cognition. These recordings are made possible by the clinical need to determine the position of epileptic foci, for which depth electrodes are temporarily implanted into the brains of patients with suspected focal epilepsy. With this setup, single-neuron recordings can be obtained using microwires protruding from....
1. Participants
To illustrate the usage of the above-mentioned method, we next briefly describe a use-case that we recently published8. We recorded 228 single neurons from the human medial temporal lobe (MTL; amygdala and hippocampus) while the patients were performing a visual search task (Figure 3A, B). During this task, we investigated whether the activity of neurons differentiated between fixations on targets and distractors.
.......In this protocol, we described how to employ single-neuron recordings with concurrent eye tracking and described how we used this method to identify target neurons in the human MTL.
The setup involves three computers: one executing the task (stimulus computer), one running the eye tracker, and one running the acquisition system. To synchronize between the three systems, the parallel port is used to send TTL triggers from the stimulus computer to the electrophysiology system (
The authors declare no conflict of interest.
We thank all patients for their participation. This research was supported by the Rockefeller Neuroscience Institute, the Autism Science Foundation and the Dana Foundation (to S.W.), an NSF CAREER award (1554105 to U.R.), and the NIH (R01MH110831 and U01NS098961 to U.R.). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. We thank James Lee, Erika Quan, and the staff of the Cedars-Sinai Simulation Center for their help in producing the demonstration video.
....Name | Company | Catalog Number | Comments |
Cedrus Response Box | Cedrus (https://cedrus.com/) | RB-844 | Button box |
Dell Laptop | Dell (https://dell.com) | Precision 7520 | Stimulus Computer |
EyeLink Eye Tracker | SR Research (https://www.sr-research.com) | 1000 Plus Remote with laptop host computer and LCD arm mount | Eye tracking |
MATLAB | MathWorks Inc | R2016a (RRID: SCR_001622) | Data analysis |
Neuralynx Neurophysiology System | Neuralynx (https://neuralynx.com) | ATLAS 128 | Electrophysiology |
Osort | Open source | v4.1 (RRID: SCR_015869) | Spike sorting algorithm |
Psychophysics Toolbx | Open source | PTB3 ( RRID: SCR_002881) | Matlab toolbox to implement psychophysical experiments |
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