Is there a brainstem substrate for action selection?

Abstract

The search for the neural substrate of vertebrate action selection has focused on structures in the forebrain and midbrain, and particularly on the group of sub-cortical nuclei known as the basal ganglia. Yet, the behavioural repertoire of decerebrate and neonatal animals suggests the existence of a relatively self-contained neural substrate for action selection in the brainstem. We propose that the medial reticular formation (mRF) is the substrate's main component and review evidence showing that the mRF's inputs, outputs and intrinsic organization are consistent with the requirements of an action-selection system. The internal architecture of the mRF is composed of interconnected neuron clusters. We present an anatomical model which suggests that the mRF's intrinsic circuitry constitutes a small-world network and extend this result to show that it may have evolved to reduce axonal wiring. Potential configurations of action representation within the internal circuitry of the mRF are then assessed by computational modelling. We present new results demonstrating that each cluster's output is most likely to represent activation of a component action; thus, coactivation of a set of these clusters would lead to the coordinated behavioural response observed in the animal. Finally, we consider the potential integration of the basal ganglia and mRF substrates for selection and suggest that they may collectively form a layered/hierarchical control system.

Parkinson's disease: Acquired frailty of archaic neural networks?

“…By connecting to multiple spinal levels, the mRF controls the axial musculature of the trunk, neck and face [93]. It also controls the activity of central pattern generators ("oscillators"), located in the spinal cord [91][92][93]. These functionally connected neurons cyclically activate motor neurons, even in the absence of descending commands from higher centers [93,94].…”

“…Repeated motor activities like locomotion, respiration and mastication are also linked to the medial reticular formation (mRF), which, below the basal ganglia, is another, more basic, "central switch" for action selection [91]. By connecting to multiple spinal levels, the mRF controls the axial musculature of the trunk, neck and face [93].…”

The Neuromodulatory System: A Framework for Survival and Adaptive Behavior in a Challenging World

“…In contrast, the present article proposes a specific shift in synaptic signaling (see Figure 4a). Prescott and his colleagues have developed models of the basal ganglia and more recently the brainstem that demonstrate action selection and switching behavior (Gurney, Prescott, & Redgrave, 2001a, 2001bGurney, Prescott, Wickens, & Redgrave, 2004;Humphries, Gurney, & Prescott, 2007;Prescott, Montes Gonzalez, Gurney, Humphries, & Redgrave, 2006). Although these models do not explicitly include neuromodulation or plasticity, they show that action selection and switching behavior can emerge from the unique anatomy and dynamics of these structures.…”

MIRO: A Robot “Mammal” with a Biomimetic Brain-Based Control System

“…Candidate structures include the midbrain reticular formationÑwhich may be important in integrating behavior within the brainstem, and in regulating behavior during early developmentÑand the basal ganglia, a group of mid-and forebrain structures that we have argued play a critical role in action selection. We have previously developed several embodied models of these brain systems (see figure 1) and have demonstrated their sufficiency to generate appropriate behavioral sequences for mobile robots engaged in activities such as simulated foraging [4,20]. [4] embedded a model of the vertebrate basal ganglia in a table-top robot and showed its ability to control action selection and behavioural sequencing for a simulated foraging task.…”