DOI: 10.6078/d1fm6s
title: Data for: Hybrid dedicated and distributed coding in PMd/M1 provides separation and interaction of bilateral arm signals

description: Pronounced activity is observed in both hemispheres of the motor cortex
 during preparation and execution of unimanual movements. The
 organizational principles of bi-hemispheric signals and the functions they
 serve throughout motor planning remain unclear. Using an instructed-delay
 reaching task in monkeys, we identified two components in population
 responses spanning PMd and M1. A “dedicated” component, which segregated
 activity at the level of individual units, emerged in PMd during
 preparation. It was most prominent following movement when M1 became
 strongly engaged, and principally involved the contralateral hemisphere.
 In contrast to recent reports, these dedicated signals solely accounted
 for divergence of arm-specific neural subspaces. The other “distributed”
 component mixed signals for each arm within units, and the subspace
 containing it did not discriminate between arms at any stage. The
 statistics of the population response suggest two functional aspects of
 the cortical network: one that spans both hemispheres for supporting
 preparatory and ongoing processes, and another that is predominantly
 housed in the contralateral hemisphere and specifies unilateral output.
description: Unit activity was collected using 24-32 channel multi-site probes
 (V-probe - Plexon Inc, Dallas, TX), with 15um diameter electrode contacts
 separated by 100um and positioned axially along a single shank. Probes
 were lowered deep enough to cover roughly the full laminar structure of
 cortex (Fig 2B-C). The depth of insertion was determined by (1)
 measurements of the dural surface prior to recording, and (2) presence of
 spiking activity across all channels. 2 probes were typically inserted in
 each hemisphere daily and removed at the end of the session, one in PMd
 and one in M1. A total of 12 insertion points across PMd and M1 of each
 hemisphere were used across 13 recording sessions in Monkey O, and 6
 insertion points across 7 sessions for Monkey W (Fig 2A). 
 Neural data were recorded using the OmniPlex Neural Recording
 Data Acquisition System (Plexon Inc, Dallas, TX). Spike sorting was
 performed offline (Offline Sorter – Plexon Inc, Dallas, TX). Single-unit
 waveforms were isolated in multi-dimensional feature space (including
 principal components, non-linear energy, waveform amplitudes) and rejected
 if either (1) the waveform clusters were not stable over the course of the
 session, (2) &gt;0.4% of inter-spike-intervals were below 1ms, or (3)
 they were clearly repeats of a unit identified on an adjacent channel as
 determined visually by coincident spiking. To fully ensure that units were
 not double logged, we eliminated one member of any pair of units that had
 a firing rate correlation above 0.9 and were within two channels of each
 other. For population level analyses (PCA, LDA), a small number of
 multi-units were included. A multi-unit was defined by waveform clusters
 that separated from the noise cluster and were stable over time, but did
 not quite meet the inter-spike-interval criteria or contained what might
 be multiple unit clusters that could not be easily separated. For monkey
 O, the average proportion of multi-units in each single session population
 sample was 17%, ranging 12-25%. For monkey W, average 20%, ranging
 12-32%. Spiking data were binned in 20ms
 non-overlapping bins, square-root transformed to stabilize variance, and
 smoothed with a 50ms gaussian kernel for all analyses (Yu et al., 2009).
 This provided an effective sampling rate of 50Hz, with each sample time
 aligned to the center of its associated bin. The window edges were
 included in all analysis windows (e.g. 300ms windows included 16
 samples).
description: Please feel free to contact Tanner Dixon by email at
 tcd44@berkeley.edu for help with using the dataset.