Dynamic structure of motor cortical neuron co-activity carries behaviorally relevant information

We thank Jacob Reimer, Zach Haga, and Dawn Paulsen for collecting the data used in this work. Data collection and reaching task We used previously published datasets from two macaques, Monkey Rs and Monkey Rj, performing an instructed center-out reaching task (Hatsopoulos et al., 2004; O’Leary & Hatsopoulos, 2006). Subjects were trained to hold a cursor on a center target presented on a video screen using a 2D arm exoskeleton (KINARM, Kingston, Ontario). One of eight radially positioned peripheral targets was then presented and served as an Instruction cue during which time the subjects were required to keep holding the cursor on the center target. After a 1 second delay period, the peripheral target began blinking (Go cue) instructing the subjects to move the cursor to the peripheral target (Figure 1A). Trial start was 0.5 s before the instruction cue appeared, and trial termination was 0.5 s after the peripheral target was acquired. Trial inclusion depended upon target acquisition falling within 1.5s following movement onset. We also only included correct trials. Movement onset is defined as the time when the hand velocity reached 5% of the peak velocity of the movement after the Go cue. Neural data were recorded from 96-channel Utah arrays implanted in the arm/hand area of primary motor cortex (M1) on the precentral gyrus. Spike waveform snippets sampled at 30 kHz were extracted using a user-defined threshold (Cerebus BlackRock Microsystems, Salt Lake City, UT) and were sorted into individual units using Offline Sorter (Plexon, Dallas, TX). The surgical and behavioral procedures involved in this study were approved by the University of Chicago Institutional Animal Care and Use Committee.

本研究使用的数据由Jacob Reimer、Zach Haga与Dawn Paulsen采集，在此谨致谢忱。数据采集与伸手任务：本研究使用了已发表的两项数据集，来源于两只猕猴（Monkey Rs与Monkey Rj），其执行的是指令式中心-外周伸手任务（instructed center-out reaching task）（Hatsopoulos et al., 2004; O’Leary & Hatsopoulos, 2006）。受试猕猴接受训练，借助二维上肢外骨骼（2D arm exoskeleton，KINARM，加拿大安大略省金斯顿市）将光标维持在视频屏幕上呈现的中心目标位置。随后屏幕上将呈现8个径向排布的外周目标中的一个，此阶段为指令提示期，受试猕猴需保持光标停留在中心目标位置。经过1秒的延迟阶段后，外周目标开始闪烁，此为启动提示（Go cue），指示受试猕猴将光标移动至该外周目标位置（图1A）。试次开始于指令提示出现前0.5秒，终止于受试猕猴成功获取外周目标后的0.5秒。试次纳入需满足目标获取发生在运动发起后的1.5秒内，且仅保留正确完成的试次。运动发起时刻定义为：启动提示出现后，手部速度达到该次运动峰值速度的5%的时刻。神经数据通过植入于中央前回初级运动皮层（primary motor cortex, M1）上肢/手部代表区的96通道犹他阵列（Utah array）采集得到。以30 kHz采样率采集的尖峰波形片段，通过用户自定义阈值（Cerebus BlackRock Microsystems，美国犹他州盐湖城）完成提取，并借助Offline Sorter软件（Plexon，美国德克萨斯州达拉斯市）分拣为单个神经元单位。本研究涉及的外科手术与行为学实验流程已获得芝加哥大学实验动物护理与使用委员会（University of Chicago Institutional Animal Care and Use Committee）批准。