What Moves Us? Neurobiology of Motivated Behavior

Answering the seemingly simple question in the title contains fascinating complexity, beyond understanding how nerves, muscles, and bones allow us to move. The mystery lies in discovering what drives us to act with a certain purpose. That is the mission of the neurobiology of motivated behavior: to reveal the brain mechanisms that underlie our intentional acts.

Unlike reflex movements, motivated behavior is a dynamic and complex process in which biological factors such as neurotransmitters, psychological factors such as emotions, and environmental factors such as the social context interact. It is no coincidence that the word motivation, from the Latin motivus (which causes movement), captures this fundamental essence. Today we know that its meaning transcends mere physical movement and comprises a sophisticated neurobiological decision-making system.

In this system, the brain fulfills at least three crucial functions: it evaluates possible targets, anticipates potential rewards, and mobilizes the resources necessary to act. This mechanism is not exclusive to human beings. From the small insect in search of food, to the mountaineer who climbs a new peak, all living beings are driven by the need to solve specific demands, whether they are physiological—such as calming hunger—or complex—such as achieving personal goals.

The fundamental question addressed by this discipline is how organisms transform “motives” into concrete actions. To answer it, science investigates how the brain detects and integrates information from the environment, constantly monitors the body’s internal states—such as the emergence of biological needs—and finally generates the appropriate motor commands to respond to those conditions. This exquisite neurobiological process explains why we pursue everything, from the most basic needs to the most intricate ambitions, revealing the complex interplay between mind, body, and environment that underpins all of our behavior.

Feeding behavior is an ideal model for exploring the neurobiological principles of motivation, as it naturally integrates physiological needs, cognitive processes, and neural mechanisms. This primordial behavior clearly reveals how the brain transforms internal demands into coordinated, targeted actions. Let’s take two examples: foraging and hunting. In the first, during the search for food, animals develop flexible behavioral strategies that allow them to navigate their environment, establish efficient routes to food sources, and estimate the nutritional value of the food found. In addition, they keep this information in memory and are thus able to reconfigure their search patterns when food runs out or changes location or when they find better options. This process involves a sophisticated integration of external signals, such as spatial location, and internal signals, such as the metabolic state of the organism. The hunting behavior, in addition to the elements described above, exemplifies the precision of the sensorimotor systems. To obtain food, the animal must process information about the position, speed, and trajectory of the prey in real time, continuously adjusting its movements.

In the central nervous system, these behaviors share a basic neural network of motivation where three main systems interact: a) homeostatic components such as the hypothalamus and the brain stem that detect physiological needs; b) the executive and sensorimotor circuits involving the prefrontal cortex for planning, as well as motor and sensory areas (along with the basal ganglia) for monitoring and precise execution of actions, and c) the dopaminergic pathways (dopamine transmission) that evaluate rewards and facilitate the association between actions and their consequences. This hierarchical organization, fundamentally oriented to satisfy the physiological-energetic demands of the organism, allows them to be transformed into adaptive behavioral responses.

Over the past 10 years, we have witnessed a technological revolution in neuroscience. The development of new molecular tools and monitoring systems allows us to know precisely the properties and elements of neural circuits. Today we can distinguish the specific genetic profiles of neuronal populations, understand their sensitivity to chemical signals, and not only observe but also manipulate their firing patterns. This allows us to map their connections and functional relationships, both within and between the circuits where they operate.

Beyond the brain, these technologies now allow us to identify the complex pathways of two-way communication between the central nervous system and the rest of the body. Technological innovations are radically transforming our understanding of how behavior emerges—from molecular and cellular interactions to integration into entire organ systems.

RESEARCH ON MOTIVATED BEHAVIOR AT UNAM
Currently, UNAM hosts several research groups that address the central question of motivated behavior using these cutting-edge methodologies. Among them is our laboratory, the A11 in the Institute of Neurobiology, which develops two complementary lines of research focused on the neural circuits of motivation.

The first line studies the logic of food reward circuits by analyzing how the brain encodes and integrates the internal state of the organism, the nutritional value of food, and the bidirectional communication between the digestive tract and the central nervous system in the regulation of eating behavior.

The second strand examines the neural circuits that control the selection and execution of movements, focusing on how behaviors are generated and adapted: through trial and error, mice progressively discover sequences of actions to obtain rewards (water and/or food).

Both approaches converge in the study of the interaction between the dopaminergic system and the basal ganglia. The latter—composed of the striatum, globus pallidus, substantia nigra, and subthalamic nucleus—constitute a key system, in which the striatum acts as a gateway, integrating sensory, motor, and cognitive signals for action selection. Its activity is modulated by dopaminergic neurons, crucial in learning processes and in the evaluation of actions.

Although our research is primarily basic science, it has clear relevance to many areas. Dysfunctions in these circuits are associated with various pathologies: movement disorders such as Parkinson’s and Huntington’s diseases, behavioral disorders like obsessive-compulsive disorder, and metabolic disorders like obesity. These circuits are also involved in addictions, where compulsive behaviors persist despite adverse consequences. Understanding these mechanisms not only expands fundamental neuroscientific knowledge, but also lays the groundwork for the development of therapeutic strategies targeting these conditions.

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