Neuromagnetic signatures of the spatiotemporal transformation for manual pointing

Abstract

Movement planning involves transforming the sensory goal representation into a command in motor coordinates. Surprisingly, the real-time dynamics of sensorimotor transformations at the whole brain level remain unknown, in part due to the spatiotemporal limitations of fMRI and neurophysiological recordings. Here, we used magnetoencephalography (MEG) during pro-/anti-wrist pointing to determine (1) the cortical areas involved in transforming visual signals into appropriate hand motor commands, and (2) how this transformation occurs in real time, both within and across the regions involved. We computed sensory, motor, and sensorimotor indices in 16 bilateral brain regions for direction coding based on hemispherically lateralized de/synchronization in the α (7-15Hz) and β (15-35Hz) bands. We found a visuomotor progression, from pure sensory codes in 'early' occipital-parietal areas, to a temporal transition from sensory to motor coding in the majority of parietal-frontal sensorimotor areas, to a pure motor code, in both the α and β bands. Further, the timing of these transformations revealed a top-down pro/anti cue influence that propagated 'backwards' from frontal through posterior cortical areas. These data directly demonstrate a progressive, real-time transformation both within and across the entire occipital-parietalfrontal network that follows specific rules of spatial distribution and temporal order..

Parieto-frontal Oscillations Show Hand Specific Interactions with Top-Down Movement Plans

“…Therefore, where applicable, we averaged or subtracted right from left targets, right from left movements, right from left hands use, and/or right from left cortical activation (signal power in a frequency band of interest) for a given brain region. This is in line with what has previously been done in recent neurophysiology (Kuang et al, 2016) and neuroimaging (Blohm et al, 2019; Cappadocia et al, 2017; Gertz & Fiehler, 2015) anti-reach studies. We then used these contrasts to highlight specificity with respect to which hand was used, if sensory processing or movement processing dominated, and whether sensory/motor processing signals were modulated by which hand was used (we call this the hand-sensory/motor code interaction effect).…”

“…These procedures are described in detail below. The data set, experimental conditions and most of the analysis pipeline have been described previously (Alikhanian et al, 2013; Blohm et al, 2019).…”

“…All further analyses were conducted in source space. We focused on previously reported independently identified regions of interest (ROIs) from the same data set (Alikhanian et al, 2013; Blohm et al, 2019); briefly, we used adaptive clustering on peak whole-brain activations in time-averaged raw, non-contrasted data to identify reliable clusters of brain activation and determined area labels that most likely corresponded to the clusters from the literature (see references in Table 1). Note that using the raw, non-contrasted data for determining ROIs was an orthogonal approach to our condition-contrasted analyses, making this a statistically valid approach (Kilner, 2013; Kriegeskorte et al, 2009).…”

“…As in our previous study (Blohm et al, 2019) our analysis took advantage of the spatial lateralization of information processing in the brain (e.g. Van Der Werf et al, 2008) to highlight our dependent variables and negate irrelevant variables.…”

“…Although various neurophysiology / imaging studies have investigated hand-target interactions in simple reach-to-target tasks, the whole-brain timing and distribution of this process remain unclear, especially for more complex, instruction-dependent motor strategies. Previously, we showed that a pro/anti-pointing instruction influences magnetoencephalographic (MEG) signals in frontal cortex that then propagate recurrently through parietal cortex (Blohm et al, 2019). Here, we contrasted left versus right hand pointing in the same task to investigate 1) which cortical regions of interest show hand specificity, and 2) which of those areas interact with the instructed motor plan.…”