Commentary: Cortical activity in the null space: permitting preparation without movement

By Mikhail A. Lebedev. 2017

447 citations recorded by the source corpus.

Kaufman et al. recently proposed a hypothesis of how cortical neuronal ensembles prepare movements without initiating them prematurely (Kaufman et al., 2014). Although novel and potentially paradigm-shifting, their model appears to contradict some of the previously reported results. Here I discuss several possible reasons for this contradiction. Kaufman et al. recorded from neuronal populations in dorsal premotor cortex (PMd) and primary motor cortex (M1), in monkeys performing center-out arm reaching movements with straight and curved trajectories. The experimental task incorporated a delay period during which monkeys could see the target but were required to withhold movement until a trigger stimulus (Figure 1A). Kaufman et al. asked how it was possible that M1 and PMd, known to project to the spinal cord and to each other (Dum and Strick, 2002), modulated their activity in in a timeand direction-dependent manner during the delay but did not induce EMG responses. While the standard explanation has been that delay-period cortical activity is a subthreshold version of movement activity (Tanji and Evarts, 1976; Weinrich and Wise, 1982; Alexander and Crutcher, 1990; Riehle and Requin, 1995; Prut and Fetz, 1999), Kaufman et al. proposed an alternative explanation. They asserted that delay-period cortical modulations were confined to a null space with respect to the linear transformation that mapped neuronal activity into movements. Mathematically, this transformation is expressed by the equation (Figure 1C):

Subfields: Cognitive Neuroscience

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Citations in the corpus

Natural continual learning: success is a journey, not (just) a destination (2021, neutral): “This is consistent with experimental findings that neural dynamics often occupy orthogonal subspaces across contexts in biological circuits [3, 14, 19, 21].”
Interpreting neural computations by examining intrinsic and embedding dimensionality of neural activity (2021, background): “For example, movement and movement preparation signals in monkeys’ motor cortex reside in orthogonal subspaces [53].”
Organizing recurrent network dynamics by task-computation to enable continual learning (2020, methodology): “Continued presence of the stimulus sets up another stable stimulus dependent ﬁxed point in an output potent [6] subspace (Figure 5B).”
Towards the neural population doctrine. (2019, background): “On the other hand, [35] ﬁnds that preparatory activity in the primate dorsal premotor cortex and primary motor cortex lives in the null space of the subspace in which movement activity resides.”
Navigating the Neural Space in Search of the Neural Code. (2017, unknown): “…low-dimensional patterns of neural activity (Brody et al., 2003; Churchland et al., 2012; Cunningham and Yu, 2014; Fitzgerald et al., 2013; Ganguli et al., 2008; Holdefer and Miller, 2002; Kaufman et al., 2014; Kobak et al., 2016; Li et al., 2016; Mante et al., 2013; Sadtler et al., 2014).”
Motor cortex embeds muscle-like commands in an untangled population response (2018, unknown): “As the network follows that three-dimensional trajectory, the figure-eight pattern can still be ‘‘read out’’ via projection, with the third dimension falling in the null space of the readout (Druckmann and Chklovskii, 2012; Kaufman et al., 2014).”
Cortical areas interact through a communication subspace (2019, unknown): “Two important recent studies have investigated the relationship between activity in motor cortex and muscles (Kaufman et al., 2014; Elsayed et al., 2016).”
Closed-loop and activity-guided optogenetic control. (2015, unknown): “…Pfau et al., 2013) are desirable for their consistency with current models of low-rank state evolution and common-input properties in observed brain dynamics (Shenoy et al., 2013; Mante et al., 2013; Kaufman et al., 2014; Churchland et al., 2012; Harvey et al., 2012; Yu et al., 2006; Sahani, 1999).”
Cognition is an emergent property (2024, unknown): “During motor preparation, cortical activity evolves within dimensions that avoid the subspaces that, during motor execution, drive downstream motor cortex or muscles [47].”