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1. The role of conjunctive representations in stopping actions

   Kikumoto, A. (October 2021, Psychological science)

   null (Ed.)

   Action selection appears to rely on conjunctive representations that nonlinearly integrate task- relevant features (Kikumoto & Mayr, 2020). We test here the flip-side of this hypothesis that such representations are also intricately involved during attempts to stop an action––a key aspect of action regulation. We tracked both conjunctive representations and those of constituent rule, stimulus, or response features through trial-by-trial representational similarity analysis of the EEG signal in a combined, rule-selection and stop-signal paradigm. Across two experiments with student participants (N = 57), we found (a) that the strength of decoded conjunctive representations prior to the stop-signal uniquely predicted trial-by-trial stopping success (Exp. 1) and (b) that these representations were selectively suppressed following the onset of the stop-signal (Exp. 1 and 2). We conclude that conjunctive representations are key to successful action execution and therefore need to be suppressed when an intended action is no longer appropriate. 

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2. The Role of Conjunctive Representations in Stopping Actions

   https://doi.org/10.1177/09567976211034505  

   Kikumoto, Atsushi; Sameshima, Tesufuaishin; Mayr, Ulrich (February 2022, Psychological Science)

   Action selection appears to rely on conjunctive representations that nonlinearly integrate task-relevant features. Here, we tested a corollary of this hypothesis: that such representations are also intricately involved during attempts to stop an action—a key aspect of action regulation. We tracked both conjunctive representations and those of constituent rule, stimulus, or response features through trial-by-trial representational similarity analysis of the electroencephalogram signal in a combined rule-selection and stop-signal paradigm. Across two experiments with student participants ( N = 57), we found (a) that the strength of decoded conjunctive representations prior to the stop signal uniquely predicted trial-by-trial stopping success (Experiment 1) and (b) that these representations were selectively suppressed following the onset of the stop signal (Experiments 1 and 2). We conclude that conjunctive representations are key to successful action execution and therefore need to be suppressed when an intended action is no longer appropriate. 

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3. Conjunctive representations that integrate stimuli, responses, and rules are critical for action selection

   https://doi.org/10.1073/pnas.1922166117  

   Kikumoto, Atsushi; Mayr, Ulrich (May 2020, Proceedings of the National Academy of Sciences)

   People can use abstract rules to flexibly configure and select actions for specific situations, yet how exactly rules shape actions toward specific sensory and/or motor requirements remains unclear. Both research from animal models and human-level theories of action control point to the role of highly integrated, conjunctive representations, sometimes referred to as event files. These representations are thought to combine rules with other, goal-relevant sensory and motor features in a nonlinear manner and represent a necessary condition for action selection. However, so far, no methods exist to track such representations in humans during action selection with adequate temporal resolution. Here, we applied time-resolved representational similarity analysis to the spectral-temporal profiles of electroencephalography signals while participants performed a cued, rule-based action selection task. In two experiments, we found that conjunctive representations were active throughout the entire selection period and were functionally dissociable from the representation of constituent features. Specifically, the strength of conjunctions was a highly robust predictor of trial-by-trial variability in response times and was selectively related to an important behavioral indicator of conjunctive representations, the so-called partial-overlap priming pattern. These results provide direct evidence for conjunctive representations as critical precursors of action selection in humans. 

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4. Synaptic integration of somatosensory and motor cortical inputs onto spiny projection neurons of mice caudoputamen

   https://doi.org/10.1111/ejn.16538  

   Sampathkumar, Vandana; Koster, Kevin P; Carroll, Briana J; Sherman, S Murray; Kasthuri, Narayanan (October 2024, European Journal of Neuroscience)

   Abstract The basal ganglia play pivotal roles in motor control and cognitive functioning. These nuclei are embedded in an anatomical loop: cortex to basal ganglia to thalamus back to cortex. We focus here on an essential synapse for descending control, from cortical layer 5 (L5) onto the GABAergic spiny projection neurons (SPNs) of the caudoputamen (CP). We employed genetic labeling to distinguish L5 neurons from somatosensory (S1) and motor (M1) cortices in large volume serial electron microscopy and electrophysiology datasets to better detail these inputs. First, M1 and S1 synapses showed a strong preference to innervate the spines of SPNs and rarely contacted aspiny cells, which are likely to be interneurons. Second, L5 inputs commonly converge from both areas onto single SPNs. Third, compared to unlabeled terminals in CP, those labeled from M1 and S1 show ultrastructural hallmarks of strong driver synapses: They innervate larger spines that were more likely to contain a spine apparatus, more often had embedded mitochondria, and more often contacted multiple targets. Finally, these inputs also demonstrated driver‐like functional properties: SPNs responded to optogenetic activation from S1 and M1 with large EPSP/Cs that depressed and were dependent on ionotropic but not metabotropic receptors. Together, our findings suggest that individual SPNs integrate driver input from multiple cortical areas with implications for how the basal ganglia relay cortical input to provide inhibitory innervation of motor thalamus. 

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5. The functional role of the striatum as an action evaluation circuit: a network-level theory

   Drammis, Sabrina; Lynch, Nancy; Friedman, Alexander (June 2024, 10th workshop on Biological Distributed Algorithms (BDA))

   Action selection is important for species survival. The basal ganglia, a subcortical structure, has long been thought to play a crucial role in action selection and movement initiation. Classical theories suggest that an important role of the striatum, the input region of the basal ganglia, is to select actions to be performed based on cortical projections carrying action information. However, thanks to recent progress in neural recording techniques, new experimental evidence suggests that the striatum does not perform action selection. Rather, the striatum plays an advisory role. Thus the classical theories of the basal ganglia need to be revisited and revised. As a rst step, in this work we hypothesize a new computational role for the striatum. We present a network-level theory in which the striatum transforms cortical action bids into action evaluations. Based on the region’s neural circuitry, we theorize that the role of the striatum is to transform bids to action values that are normalized, contrast-enhanced, orthogonalized, and encoded as continuous values through the use of two separate neuron populations with bipolar tuning and both feedforward and collateral inhibitory mechanisms. We simulate our network and investigate the role of the network components in its dynamics. Finally, we compare the behavior of our network to previous literature on decision-making behavior in rodents and primates. 

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