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. 2012 Feb 23;73(4):829-41.
doi: 10.1016/j.neuron.2011.12.035.

Only coherent spiking in posterior parietal cortex coordinates looking and reaching

Heather L Dean  1 , Maureen A Hagan, Bijan Pesaran
Affiliations

Only coherent spiking in posterior parietal cortex coordinates looking and reaching

Heather L Dean et al. Neuron. .

Abstract

Here, we report that temporally patterned, coherent spiking activity in the posterior parietal cortex (PPC) coordinates the timing of looking and reaching. Using a spike-field approach, we identify a population of parietal area LIP neurons that fire spikes coherently with 15 Hz beta-frequency LFP activity. The firing rate of coherently active neurons predicts the reaction times (RTs) of coordinated reach-saccade movements but not of saccades when made alone. Area LIP neurons that do not fire coherently do not predict RT of either movement type. Similar beta-band LFP activity is present in the parietal reach region but not nearby visual area V3d. This suggests that coherent spiking activity in PPC can control reaches and saccades together. We propose that the neural mechanism of coordination involves a shared representation that acts to slow or speed movements together.

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Figures

Figure 1
Figure 1. Schematic illustrating link between preparation and combined movement RTs
(a) Correlations between saccade and reach RTs when movements are prepared separately. Upper right: Dark points show RTs during groups of trials when saccade preparation is low. Gray points show RTs during groups of trials when saccade preparation is high. Lower right: Dark points show RTs during groups of trials when reach preparation is low. Gray points show RTs during groups of trials when reach preparation is high (b) Correlations between saccade and reach RTs when movement preparation is coordinated. Dark points show RTs during groups of trials when coordinated preparation is low. Gray points show RTs during groups of trials when coordinated preparation is high. In this figure, RTs are illustrative and do not reflect experimental data.
Figure 2
Figure 2. Behavioral task and RT correlations
(a) Reach and saccade task. (b) Saccade only task. (c) Scatter plot of reach RT and saccade RT for each trial during the Reach and saccade task in an example session. Histograms show the distributions of each RT. Asterisk denotes mean RT for each effector.
Figure 3
Figure 3. Recording sites and example area LIP data
(a) Structural magnetic resonance images showing recording sites for fields in Monkey J. (b) i. Trace from example area LIP recording filtered to show LFP (red) and spiking activity (black). ii. Color map presents average percent change in spectrum for example field during the Reach and saccade task aligned on target onset and on saccade start for preferred direction. Horizontal black line above data in i. and ii. indicates the time of the analysis shown in d. (c) Example data as in b for the null direction, (d) Line plot of spectral density at each frequency for preferred and non-preferred directions 1.5 s after target onset in the Reach and saccade task for the example field shown in b and c (red) as well as baseline activity in the 0.5 s before target onset (blue). (e) Line plot of the change from baseline for preferred (solid line) versus null (dashed line) directions. Gray indicates 95% confidence interval in d and e. See also Figure S1.
Figure 4
Figure 4. LFP reaction time analysis in area LIP
(a) Reach and saccade task. Mean fractional change over baseline during delay for 33% of trials with fastest SRT (solid) and slowest SRT (dashed) before movements to the preferred direction; (b) 33% of trials with fastest RRT (solid) and 33% of trials with slowest RRT (dashed) before movements to the preferred direction; (c) same as a for null direction; (d) Same as b for null direction, (e) Saccade only task Mean fractional change over baseline during delay for 33% of trials with fastest SRT (solid) and 33% of trials with slowest SRT (dashed) for preferred direction; (f) same as e for null direction. In each panel, gray shading indicates the standard error of the mean.
Figure 5
Figure 5. Encoding of coordinated movement RTs in spiking activity coherent with LFP in area LIP
(a) Population average peri-stimulus time histograms (PSTHs) of firing rate during reach and saccade trials for cells with spiking activity that is coherent (left; Coherent cells) or not coherent (right; Not coherent cells) with LFP activity at 15 Hz. Spike-field coherence was calculated during the late delay period (horizontal bar). Preferred direction trials (solid lines) and null direction trials (dashed) are plotted separately, (b) Population average PSTHs for the same cells in a during the Saccade alone task. Conventions as in a. (c) Probability of correct classification of trials in the preferred direction as fast or slow RT trials based on firing rate in the 8 cells with the highest RT selectivity based on an ANOVA. Dashed line indicates chance performance. Error bars indicate standard deviation. * indicates p < 0.05, ** p < 0.01. See also Figure S2.
Figure 6
Figure 6. Selectivity for both SRT and RRT in area LIP
(a) Scatter plot of selectivity of activity at 15 Hz for SRT against selectivity of activity at 15 Hz for RRT. Selectivity is measured as a z-score for difference in power against the null hypothesis that there is no change in power. (b) Same as a for activity at 45 Hz. Histograms show the marginal distributions. Each dot represents data from one LFP session.
Figure 7
Figure 7. Time course of RT selectivity in area LIP, PRR and V3d
(a) Line plot of correlation of activity (z-score) in area LIP at 15 Hz with RRT (top row) and with SRT (bottom row) aligned on target onset and go cue before reach-and-saccade movements to the preferred direction. (b) Same as a for PRR. (c) Same as a for V3d. In each panel, gray indicates 95% confidence interval.
Figure 8
Figure 8. Directional selectivity in area LIP, PRR and V3d
(a) Time course of average z-score aligned on target onset and on saccade start for 15 Hz, beta-band LFP power in area LIP. (b) Same as a for 45 Hz gamma frequency band. (c) Time course of average z-score aligned on target onset and on saccade start for 15 Hz, beta-band LFP power in PRR. (d) Same as c for 45 Hz gamma frequency band. (e) Time course of average z-score aligned on target onset and on saccade start for 15 Hz, beta-band LFP power in V3d. (f) Same as e for 45 Hz, gamma frequency band. Reach and saccade (solid). Saccade only (dashed). Gray indicates 95% confidence interval. See also Figures S3-5.
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