Chapter 14: The Secret to Dishwashing Robots

Chapter Overview:

• Main Focus: This chapter explores the evolution of the motor cortex and its role in planning and executing complex movements. Bennett challenges the traditional view of the motor cortex as simply a "commander" of muscles, proposing instead that it functions as a predictive simulator of movement, enabling fine motor control, motor learning and flexible adaptation. He uses the provocative example of dishwashing robots, which as of 2023 still do not exist, to demonstrate that something assumed to be relatively easy is, in fact, remarkably hard, highlighting that fine motor control in mammals may be more sophisticated and complex than previously thought (Bennett, 2023, p. 221).
• Objectives:
• Reframe the traditional understanding of the motor cortex.
• Describe the evolution of the motor cortex in mammals and primates.
• Link the motor cortex to the neocortex's simulation capabilities.
• Introduce the concepts of motor planning, mental rehearsal, and the motor hierarchy.
• Explain how these concepts relate to building more sophisticated and adaptable robots.
• Fit into Book's Structure: This chapter extends the discussion of the neocortex (Chapter 11-13) by focusing on its role in controlling movement, foreshadowing the discussion of primate tool use, social learning, and imitation learning (Ch. 17 & 18), which are all highly dependent on fine motor control (Bennett, 2023, p. 241). It provides a bridge between the brain's internal models of the world and its ability to act upon those models, setting the stage for the final breakthroughs in primate and human intelligence.

Key Terms and Concepts:

• Motor Cortex: A region of the neocortex involved in planning, controlling, and executing voluntary movements. Relevance: The motor cortex is the central focus of the chapter, and Bennett challenges the conventional understanding of its function.
• Sensorimotor Planning: The ability to plan and execute complex movements that involve both sensory input and motor output. Relevance: This ability is presented as a key function of the motor cortex.
• Mental Rehearsal: The process of mentally simulating an action without actually performing it. Relevance: Mental rehearsal is shown to improve motor performance, supporting the idea that the motor cortex is involved in simulation.
• Motor Hierarchy: The organization of motor control into a hierarchy of levels, from high-level goals to low-level muscle commands (Bennett, 2023, p. 226-227). Relevance: This hierarchy is linked to the hierarchical structure of the neocortex and the interplay between the prefrontal cortex, premotor cortex, and motor cortex.
• Model-Based Control: Motor control that relies on an internal model of the body and the environment to predict the consequences of movements. Relevance: This type of control is linked to the motor cortex's simulation capabilities.
• Model-Free Control: Motor control that relies on learned associations between sensory inputs and motor outputs, without an explicit internal model. Relevance: Model-free control is associated with habits and automated movements and is contrasted with model-based control.
• Alien Hand Syndrome: A neurological disorder in which a person's hand seems to act on its own, without their conscious control. Relevance: This syndrome, which is observed in patients with damage to their premotor cortex, illustrates how damage to certain areas of the frontal neocortex can impair this coordination between intent and action, which highlights the importance of the premotor cortex in enabling an animal to correctly execute the steps required for an intended outcome or plan (Bennett, 2023, p. 229).

Key Figures:

• Karl Friston: A neuroscientist known for his work on the free energy principle. Relevance: Friston's concept of active inference is applied to motor control, suggesting that the motor cortex generates predictions of movement rather than direct commands. Bennett uses the analogy of the motor cortex not being a commander but rather a puppeteer, by highlighting the difference between the more traditional notion that the motor cortex sends explicit commands to muscles (like a commander) versus the notion that the motor cortex sends signals to muscles to align with its predictions of how those muscles should move (like a puppeteer) (Bennett, 2023, p. 224).
• Antonio Damasio: A neuroscientist whose work focuses on the neural basis of emotion and decision-making. Relevance: Damasio's studies of patients with prefrontal cortex damage provide insights into the role of this brain region in planning and intention, highlighting that damage to certain areas of the frontal cortex can result in paralysis or the loss of intentionality altogether. He uses Damasio’s observations to argue that the prefrontal cortex evolved to control what is being simulated, whereas the neocortex is what renders the simulations (Ch. 11) (Bennett, 2023, p. 204-205). And that, therefore, though both areas are similar in structure (both are neocortex), their function differs (Bennett, 2023, p. 207).

Central Thesis and Supporting Arguments:

• Central Thesis: The motor cortex is not simply a commander of muscles, but a predictive simulator of movement, enabling flexible, adaptable, and precise motor control through a hierarchical system of sensorimotor planning, by simulating the expected sensory outcomes of those movements (Bennett, 2023, p. 224). The author argues that this is how mammals and primates learn complex sequences of actions such as reaching for food or navigating complex terrain, and how primates use this same ability for fine motor tasks and tool use (Bennett, 2023, p. 226).
• Supporting Arguments:
• Fine motor skills: Mammals, particularly primates, exhibit a high degree of fine motor control, which would be difficult to achieve with a purely reactive, model-free system.
• Mental rehearsal: Mentally rehearsing movements improves performance, suggesting a role for simulation in motor control.
• Hierarchical organization: The hierarchical structure of the motor system, from high-level goals to low-level muscle commands, aligns with the neocortex's hierarchical organization and its ability to simulate at different levels of abstraction. This allows the premotor cortex and motor cortex to work in parallel with the more automatic behavior-selection mechanisms in the basal ganglia. The premotor and motor cortices learn new movements which are slow and deliberative at first, and then once they have been performed enough times they are transferred to the basal ganglia to automate and optimize for energetic and computational efficiency (Bennett, 2023, p. 227-230).
• Model-based control: Evidence from neuroscience suggests that the motor cortex generates predictions of movement, not just commands to muscles.
• Evolutionary perspective: The motor cortex emerged in placental mammals, coinciding with the development of more complex motor behaviors, and is not present in earlier lineages (Bennett, 2023, p. 222-223). This emphasizes a crucial evolutionary distinction between the brains of early mammals and the brains of modern primates.

Observations and Insights:

• The link between perception and action: The motor cortex is closely linked to the somatosensory cortex, suggesting an integration of sensory input and motor output in planning and executing movements.
• The importance of feedback: Motor control is not a one-way street; the brain constantly receives feedback from the body and the environment to adjust and refine its movements.
• The role of intention in motor control: The prefrontal cortex's influence on the motor hierarchy highlights the importance of goals and intentions in shaping movement. This is connected to the earlier discussion of ‘intent’ as being an emergent property of aPFC models of valence (Ch. 12) (Bennett, 2023, p. 209).

Unique Interpretations and Unconventional Ideas:

• The motor cortex as a predictive simulator: This challenges the traditional view of the motor cortex as a simple commander of muscles.
• The link between the motor cortex, planning, and the "first move" advantage: This ties the evolution of the motor cortex to the ecological pressures faced by early mammals, including their small size and reliance on strategic planning for survival (Bennett, 2023, p. 243).

Problems and Solutions:

Categorical Items:

Bennett categorizes motor behaviors as either goal-directed (model-based) or habitual (model-free) by distinguishing how each of these methods maps to specific neural mechanisms. Goal-directed behavior requires both the frontal and sensory neocortices, whereas habitual behavior may only require the basal ganglia (Bennett, 2023, p. 209).

Literature and References:

• Works by Friston and Damasio are cited.
• Research on the motor cortex, sensorimotor planning, and motor control in various species is referenced.

Areas for Further Research:

• The precise neural mechanisms underlying the motor cortex's simulation abilities require further investigation.
• The interplay between model-based and model-free motor control in different contexts is an open question.
• The development of more sophisticated and adaptable robots can be inspired and informed by greater understanding of the subtleties of motor control in mammals (Bennett, 2023, p. 221).

Critical Analysis:

• Strengths: The chapter offers a novel and compelling perspective on the motor cortex, challenging traditional views and integrating insights from neuroscience, psychology, and robotics.
• Weaknesses: The chapter simplifies complex neural processes and the evidence for predictive simulation in the motor cortex is still developing.

Practical Applications:

• Understanding the principles of motor planning and control can inform the design of more sophisticated and adaptable robots, prosthetic devices, and rehabilitation therapies.

Connections to Other Chapters:

• Chapter 11, 12, and 13 (Neocortex, Simulating, Model-Based Learning): This chapter extends the discussion of the neocortex and its simulation abilities by focusing specifically on its role in motor control. It links model-based learning and simulation to the motor cortex, specifically to fine motor control of actions in the world, which then drives the evolutionary selection of particular neural circuits. Those animals whose brains dedicated more neocortical real estate to areas for finer motor control were more successful because they were better able to perform the complex sequences of actions required to perform more sophisticated and efficient behaviors, and thus these brains had more energy and resources and were also more likely to survive (Bennett, 2023, p. 221). These arguments are particularly apparent in his discussion of the hierarchical organization of the motor system and how it coordinates with more automatic processes in other brain regions (Bennett, 2023, p. 226-227). Model-based learning and simulation gives placental mammals an ‘edge’ by allowing them to plan and simulate ahead of time and learn from experience vicariously without the need to always learn “in person.” But by using the prefrontal cortex to select what and when to simulate, placental mammals could conserve computational resources—they could be deliberative when it was valuable and become automatic and habitual (model-free) when it made sense to do so. This allows for the development of complex behaviors with great precision and flexibility, but also maximizes efficiency by automating what no longer requires deliberation and simulation. And so, from these complex mechanisms of simulation emerges something previously discussed as an essential feature of intelligence: how to make goals and create habits (or as the author calls it, the “inner duality”) of mammals (Bennett, 2023, p. 215). This is a central argument in the chapter and connects model-based reinforcement learning to the capacity of animals to not only learn, but also to make long-term plans and develop intentionality, setting up the later discussions of uniquely human cognitive capacities such as language.
• Chapter 16 (Arms Race for Political Savvy): This chapter foreshadows how the sophisticated motor control enabled by the neocortex and motor cortex played a crucial role in the development of tool use, a key factor in human evolution and the cognitive arms race of primates more generally.

Surprising, Interesting, and Novel Ideas:

• The motor cortex as a predictor of movement, not a commander: This perspective challenges traditional views of motor control, emphasizing the role of internal models and simulation (Bennett, 2023, p. 223-224).
• The importance of mental rehearsal in improving motor skills: The fact that simply imagining movements can enhance performance suggests a strong link between the motor cortex, simulation, and learning (Bennett, 2023, p. 225). This supports his prior argument in Ch. 11 about how closely perception and imagination are wired in the neocortex, suggesting that this same wiring evolved as a general mechanism for supporting learning by simulation, not merely recognition of things in the world.
• The link between the motor hierarchy and the hierarchical structure of the neocortex: This connects motor control to broader principles of cortical organization and function (Bennett, 2023, p. 226-231). He uses the emergence of the motor cortex in placental mammals to show how even the neocortex itself can be subject to this same hierarchical control, whereby higher-level areas in the neocortex can direct lower levels, but these lower levels can also, in turn, learn how to perform certain tasks automatically without need for “top-down” neocortical control. He argues that this explains goal-directed and habit-directed behavior and highlights how goals and habits represent two sides of the same coin.

Discussion Questions:

• How does Bennett's view of the motor cortex differ from traditional understandings of its function?
• What are the implications of the motor cortex being a predictive simulator for our understanding of free will and agency?
• How might mental rehearsal be used to improve athletic performance, rehabilitation after injury, or the learning of new skills?
• What are the challenges of designing robots with hierarchical motor control systems?
• How does our understanding of the motor cortex inform the development of brain-computer interfaces and other assistive technologies?

Visual Representation:

[Intent (PFC)] --> [Premotor Cortex (Subgoals)] --> [Motor Cortex (Simulation & Prediction)] --> [Motor Commands] --> [Muscles] --> [Movement] --> [Sensory Feedback]

TL;DR: