1. Can You Think Without Words? Inner Voices and Mental Pictures
When calculating 17 × 6 in your head, some people whisper it, while others picture the numbers. If you have an "inner voice," it feels like that voice is doing the thinking. A paper published in Nature in 2024 challenged this view. It argues that language is a tool for sharing knowledge and feelings with others, rather than a tool for thinking itself [1]. One piece of support comes from people with language disorders. Even when the disability is severe enough to disrupt word processing, abilities like solving math problems, playing chess, or planning for the future may be preserved, according to an MIT introduction article [2].
This suggests that while words are very useful for passing thoughts to others, they might not be essential for thinking itself. However, this is just one paper’s claim. Whether language acts as a scaffold for creating complex concepts is still debated. Also, reports say abilities "may be preserved" in people with severe language disorders; it does not mean everyone will definitely retain them. If words are not required, what actually moves inside the head?
2. How Neurons Passing Signals Support Thinking
The work of thinking is supported by neurons (nerve cells) in the brain passing signals to each other. A booklet published around 2002 by a US national agency describes neurons as "messengers of information," carrying it via electrical and chemical signals [3]. Inside a cell, electrical signals travel. However, cells are not perfectly connected; there is a small gap at the junction called a synapse. When a signal reaches this gap, chemicals called neurotransmitters cross over to pass the message to the next cell [3]. It is similar to passing notes hand-to-hand from the front of a classroom to the back, but in reality, countless cells are passing signals separately.
The number and connections of neurons may not stay the same. The same booklet mentions a study where male canaries showed a dramatic increase in forebrain neuron numbers during breeding season when learning new songs [3]. Note that this is from a 2002-era booklet. Whether new nerve cells are born in the adult human brain has been a subject of disagreement among researchers since that time.
Do electrical signals and gaps alone allow calculations like 17 × 6? Where does the brain keep the intermediate step, such as "7 times 6 is 42"? Let’s look at where these temporary notes are placed.
3. Working Memory: Where the Brain Keeps Temporary Notes While Thinking
To solve 17 × 6 mentally, you might first hold onto 60 (from 10 × 6) and then add 42 (from 7 × 6). The ability to keep information active only while thinking is called working memory. Records from a workshop by the US National Institute of Mental Health (NIMH) distinguish working memory from long-term memory. Long-term memory has a longer retention time but can be hard to retrieve, and it is sometimes recalled automatically [4]. There are also trends in brain circuits: circuits maintaining working memory are thought to be deeply involved with the front part of the brain (frontal), while circuits directing attention are linked near the top of the head (parietal) [4].
In 2007, NIMH announced that a chain of molecular interactions keeping temporary location memories alive had been identified in monkeys [5]. Furthermore, a 2021 report from the US National Eye Institute stated that groups of neurons maintaining working memory content also reflect the uncertainty of that memory [6]. This means the feeling of "it’s around here" is reflected in brain activity. Even without words, there are notes and estimates of certainty. Are mental images a similar function?
4. Do Mental Images Look the Same to Everyone?
Closed your eyes and picture your front door. Some people see the color of the door clearly, while others have only a vague impression. The condition where it is hard to form mental images is called aphantasia. A 2024 reanalysis combining data from 9,063 people estimated the rate at about 0.9% (less than 1 in 100 people); initial surveys alone suggested 1.2% [7]. According to University of Chicago news, such people find it difficult to draw what they see from memory, and this difference is specific to memory [8].
On the other hand, research at the University of Exeter showed that people with particularly vivid images have stronger connections between visual processing areas and the frontal lobe, which handles judgment and attention. This difference was seen in brain scans while resting [9]. This is not a matter of better or worse. Even when "thinking," the way the head is used may vary by person. What people use to think seems to differ.
Still, words are not doing nothing in the head. Let’s look at what happens in the brain when using language.
5. What Role Do Words Play in the Brain?
Even if words are not essential for thinking, they have roles in the head. MIT research showed that the brain’s language network reacts most strongly when reading complex, unfamiliar sentences where grammar changes or meanings are unexpected. Simple sentences caused almost no reaction [10]. The language network works hard to decode difficult sentences.
There are also attempts to read inner words. A study reported in 2025 created a device for four people that decoded imagined words (inner speech) from motor cortex brain activity within a 50-word vocabulary, almost in real time. The error rate when outputting sentences was reported as 14–33% [11]. This number does not mean the inner voice can be fully read. Having an inner voice is different from it being all of thinking. The Nature paper claims language is mainly for sharing thoughts with others. Whether language helps create complex thoughts is still debated.
Can you check what is in your own head at home?
6. Try It Yourself: Draw Your Front Door and Compare It to the Real One
You can try this observation at home: Close your eyes and picture your front door. Then, draw the door on paper and compare it to the real one. Check if details like the door color, shoe box position, or number of umbrella stands match. This is not a competition of skill, but a game to see what appears in drawings from memory.
Try another thing: Solve 17 × 6 in your head and write down one note about whether you said it aloud, pictured numbers, or had nothing come to mind. If you do the same calculation on another day, you might notice it is not always the same.
To read more, ask family or friends to solve the same calculation mentally and ask how they did it. If answers differ—voice, number images, or nothing—the story becomes closer. For further reading, starting with the MIT introduction article [2] makes it easier to understand the position of the main paper [1] (in English).