How To Train Your Brain: The 2026 Homunculus

You might know that it takes around 66 days for a habit to stick (Lally, Phillippa, et al., 2010). But did you know that while working toward your goals, you may also be reshaping your brain’s cortical structure? 

There exists a small, disfigured human in everyone’s head; in fact, there are two. This little figure is known as the homunculus (Penfield, Wilder, and Edwin Boldrey, 1937). The sensory homunculus represents how different parts of the body are mapped in the somatosensory cortex, while the motor homunculus reflects how movements are organized in the motor cortex. In this article, we explore how our daily activities quite literally shape our brain, and how strikingly different the 2026 homunculus might look. 

Somatosensation refers to the perception of all mechanical and physical stimuli that affect the body. It helps us perceive temperature, pressure, pain, and also to understand where our body is positioned in the three-dimensional space. Specialized sensory receptors make this possible. Mechanoreceptors, such as Meissner’s corpuscles, Merkel cells, Pacinian corpuscles and Ruffini endings can sense touch, while nociceptors detect pain (Kandel et al., Principles of Neural Science). However, these receptors are not evenly distributed across the body. Thousands are packed into areas like the lips and fingertips, making them extremely sensitive, while regions such as the thighs contain far fewer. This uneven sensory input is an important point to remember when understanding why different body parts occupy vastly different amounts of space in the brain’s cortical maps. 

Information from the somatosensory receptors travels via the spinal cord to the thalamus, a major sensory relay station, before finally entering the primary somatosensory cortex or S1 (Kandel et al., Principles of Neural Science). S1 lies on the postcentral gyrus located just behind the brain’s largest groove, the central sulcus. In contrast, the primary motor cortex lies on the precentral gyrus, just in front of this groove. While the somatosensory cortex maps incoming sensory information from different parts of the body, the motor cortex is a map of how much cortical real estate is devoted to controlling movements of a body region. It generates signals that cause muscle contractions, sends commands down the corticospinal tract, and ultimately influences the motor neurons. Both the maps are organized by body parts, and this arrangement is called somatotopy. For instance, the hand has a highly specialized representation in the somatosensory cortex. Mechanoreceptors in the skin of the hand send signals to a dedicated hand area in S1, where all our individual fingers are distinctly mapped. Each finger has a sharp, well-defined boundary (D1-D5), allowing for very precise sensory discrimination and control (Merzenich et al., 1988). 

Now, where do these homunculi come from? The answer lies in the fact that the brain has finite resources, while different parts of the body are used to very different extents. Unlike many other cells in the body, neurons largely stop dividing after early development. Therefore, our brain operates as a kind of zero-sum system: increased representation for one function often comes at the expense of another (Buonomano & Merzenich, 1998). Body regions that are used more frequently have much larger cortical representations. The homunculi, therefore, act as functional maps of the body, where the size of each body part reflects the density of sensory receptors and the importance of its use. Our fingers contain an exceptionally high number of sensory receptors, making them extremely sensitive to touch and granting them a disproportionately large representation in the cortex. This brings us to the question: if certain body parts are used far more than average, would their cortical representations change? Research says yes, and it suggests that the somatosensory cortex is highly plastic, continuously reshaping itself in response to the environment. 

Changes in the homunculus are known as functional reorganizations or cortical plasticity. A study conducted on adult owl monkeys revealed how the cortical maps of the middle and ring fingers merged when their fingers were surgically sewn together, and when unfused, the representations gradually corrected themselves (Merzenich et al., 1984; Merzenich et al., 1987). The cause of phantom limb sensations can be understood through this same principle. If you accidentally cut your finger off, the brain area that is dedicated to it doesn’t stay silent forever. Instead, neurons from neighboring cortical regions begin to form new synaptic connections within that unused territory in the S1. The homunculus reveals that the eyes, nose and face representations lie close to the hand area. Hence, touching the face might elicit a feeling that your amputated finger was being touched! Researchers hypothesize that such phantom limb sensations are largely caused due to these cortical reorganizations (Ramachandran et al., 1992; Ramachandran & Hirstein, 1998). This was the foundation of Merzenich's work ‘Brain Training’: if the map can be deformed by injury, it can be reformed by intentional practice (Buonomano & Merzenich, 1998). 

The story becomes even more intriguing when considering phantom limb pain. It has been reported that around 80% of amputees feel a phantom pain in their missing limb (Ramachandran & Hirstein, 1998). This phenomenon is caused by a combination of peripheral and central nervous system factors. Peripherally, severed nerve endings in the stump attempt to regenerate; however, without a target, they form disorganized clusters called neuromas (Vaso et al., 2014). These neuromas fire abnormal and sudden electrical signals that the brain interprets as pain. Centrally, phantom limb pain is caused due to a broken sensorimotor feedback loop (Flor et al., 2006). Normally, when the motor cortex sends a command to move, it expects sensory feedback. In amputees, the feedback is lost, which causes the brain to increase pain signals as a warning. In other words, the brain continues to expect input from a limb that no longer exists. Hence, if the left arm is amputated, the brain still needs some form of feedback that it believes is coming from the left arm. Mirror therapy treats this condition by providing the missing visual feedback, completing the loop and tricking the brain (Ramachandran & Rogers-Ramachandran, 1996). Here, the mirror is placed perpendicular to the patient’s chest, so that the reflection of the right arm appears to be the left arm itself. 

All of this shows how reformable our brains are and how easily they can be reshaped. Researchers wondered whether regular practice and training of specific body parts could lead to changes in the organization of the brain. In a study conducted by Thomas Elbert and his colleagues, they investigated the somatosensory representations of the hand area in violin players (Elbert et al., 1995). They found that the area of the brain dedicated to the left-hand fingers was significantly larger and more electrically active than in non-instrumentalists. What also mattered was the age they began playing the violin. Players who started at age 5 had much larger finger representations than those who started later. This study shows that while the brain is plastic throughout life, it is most plastic during childhood. There is even evidence that cortical reorganization can occur after just 15 to 30 minutes of daily practice (Classen et al., 1998).

However, as seen in the owl monkey studies and in human juggling experiments, the brain can easily return back to its original state, without practice (Draganski et al., 2004). Hence, “use it or lose it” isn’t just a gym phrase, it is also the golden rule of neuroplasticity. 

With that, we come to the question: what would the 2026 homunculus look like? Perhaps it would show larger representations of the eyes and the fingers, as we’re constantly glued to screens. Fine finger movements involved in scrolling, texting, and typing, along with rapid visual information processing and frequent eye saccades, would likely contribute to increased eye and finger maps. In contrast, body parts involved in movement, balance and posture, such as the legs, feet, and core, may show reduced representations due to our increasingly sedentary lifestyles. 

There’s nothing to be frightened about, though. This modern homunculus is not fixed. Just as practice can enlarge cortical maps, disuse can shrink them, and new habits can reshape them once again. We must remember that the homunculus is not just a static map of the body, but rather a reflection of how we live. So yes, don’t skip the gym today! 

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Written by Neermita Bhattacharya

References

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● Merzenich, Michael M., et al. "Variability in hand surface representations in areas 3b and 1 in adult owl and squirrel monkeys." Journal of Comparative Neurology 258.2 (1987): 281-296. 

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