Left brain vs. right brain: Fact and fiction

How does the brain work?

The brain is a complex organ that controls all bodily processes, including thought, sensory perception, and physical action. Despite weighing only 3 pounds, the human brain contains as many as 100 billion neurons.

Neurons are information messengers that use electrical and chemical impulses to transmit information around the central nervous system (CNS).

The brain processes information it receives through its neuron network and sends signals to all parts of the body to control bodily functions and respond to stimuli

Brain areas

There are several different regions of the brain that are responsible for different functions.

The cerebrum is the upper part of the brain. It has a left and right side and controls most complex processes, such as thinking, emotions, feeling, speech, and vision, among others. The cerebrum has four parts called lobes- the frontal, temporal, parietal, and occipital.

The cerebellum is another part of the brain. It mostly controls coordination and movement. Unlike the cerebrum, the cerebellum controls the same side of the body.

The diencephalon is a central portion of the brain and acts as a relay station between the brain and body, and also controls hormones. The brainstem controls most automatic functions- breathing, eye movements and facial movements. It also acts as a conduit between the brain and the body.

Left and right sides

The main point between the left and right sides of the brain is that they control movement in the opposite half of the body. For example, the left side of the brain controls physical movement in the right arms, legs, and other areas, and vice versa.

Besides this, there can be variations between people. For example, often the brain’s left half is responsible for a large number of processes, including speech. However, left-handed people have a higher chance of the right side of their brain primarily controlling language, or having language processes split across the brain hemispheres.

The left and right sides of the brain connect via the corpus callosum. This is a collection of nerve fibers that send messages between the two hemispheres.

In very rare situations, such as specific types of epilepsy surgery or certain developmental disorders, there is a lack of communication between the two hemispheres, and this can sometimes be compatible with survival, although it causes significant disability due to a lack of integration between the two hemispheres.

Left-brained vs. right-brained theory

In the 1960s, the neurobiologist Roger W. Sperry suggested that in individuals, either the right or left side of the brain is dominant, determining personality, thoughts, and behavior.

Due to the different functions of the two brain hemispheres, the idea that people can be left-brained and right-brained is appealing.

According to the dated theory, left-brained people are more:

• analytical
• logical
• detail- and fact-oriented
• numerical
• likely to think in words

By contrast, the theory suggests that right-brained people are more:

• creative
• free-thinking
• able to see the big picture
• intuitive
• likely to visualize more than think in words

What does the research say?

Research suggests that the left-brain vs. right-brain theory is incorrect. While specific parts of the brain do dominate the processing of different mental tasks, there is typically no overall dominant side.

A 2013 study assessed 3-D pictures of over 1,000 people’s brains. They measured the activity of the left and right hemispheres using an MRI scanner. Their results show that a person uses both hemispheres of the brain and does not seem to have a dominant side.

However, a person’s brain activity does differ depending on what task they are doing. Some of these differences in task processing run counter to the right/left-sided brain theory.

For example, a 2023 review described that processes occurring in the right side of the brain are essential for:

• spatial awareness during complicated calculations
• understanding numbers that contain zeros
• representing numbers nonverbally

Similarly, while the left side of the brain is the dominant force in language processing, both sides are necessary for full comprehension.

Authors of a 2020 review also report that the right side of the brain plays a key role in understanding context and non-literal cues, such as metaphors, irony, and language visualization.

Functions and characteristics of each hemisphere

Although people do not fall neatly into the categories of left-brained or right-brained, there are differences in what the left and right hemispheres do.

The left and right hemispheres control visual, motor, and sensory functions on the opposite side of the body.

The locations that control these functions are mirror images of each other, and they take up a significant portion of the two hemispheres.

• The occipital lobes: These lobes are at the back of the brain and view the opposite side of vision (not the opposite eye). The left occipital lobe views the right side of vision from both eyes, and the right occipital lobe views the left side of vision from both eyes.
• The frontal lobes: The left and right frontal lobes, especially the more forward portion of the frontal lobes, are involved in decision making. This lobe also includes Broca’s speech area. This is essential for language production and fluency
• The temporal lobe:. The temporal lobe is also the area for integrating and understanding sounds on the same side of the body.
• The motor strips: These are also known as the motor homunculus and are located at the back region of the frontal lobe. The motor strips control the movement of the opposite side of the body
• The sensory strips: These are part of the parietal lobe, right behind the motor strip, and control the sensation of the opposite side of the body.

Differences in the left and right brain hemisphere function exist in:

Emotion

While the brain uses multiple areas to process and generate emotional responses, the right side of the brain is dominant in these processes.

Language

The left brain is more active in language processing than the right. In most people, the two main language areas, known as Broca’s area and Wernicke’s area, are in the left hemisphere.

Does hemispheric dominance differ between people?

Not everyone’s brains work in the same way. Some people may primarily process language on the left side of their brain, while others may do so on the right side or symmetrically across the hemispheres.

A large 2021 study found that left-handed people often use different sides of their brains for working memory, language, vision, and hand control compared to right-handed people.

Researchers also found that left-handed people typically had more gray matter on the right side of their brains. This may be because the right side of the brain controls the dominant left hand. Gray matter is a type of tissue responsible for processing information and enabling movement, memory, and emotions.

However, both sides of the brain and communication between them are necessary for efficient functioning. People do not use one side more than the other.

Summary

The brain is a complex organ with many parts and functions. The division of these functions can differ between people. For example, the left side of the brain is primarily responsible for language and communication in most right-handed people, while this is less common in those who are left-handed.

While the two halves of the brain have different functions, people do not have a dominant side that affects their personalities and behaviors.