You’re on the phone with your mother, back in the country where you grew up. You’re telling her a story, laughing, when suddenly you stop. The word—a simple, everyday noun you’ve used a thousand times—is gone. It’s hovering just out of reach, a ghost on the tip of your tongue. In its place, your brain helpfully supplies the English equivalent, which you bat away in frustration. Finally, you give up and describe the object awkwardly until your mother supplies the word you were looking for. “Ah, right!” you say, feeling a strange mix of relief and unease.

For millions of immigrants, expatriates, and multilingual individuals, this experience is all too familiar. We tend to think of our first language, our mother tongue, as an immutable part of who we are—a bedrock of identity that can’t be shaken. But linguistics and neuroscience show us something more complex. This phenomenon of a native language becoming “rusty” is known as first language attrition, and it reveals fascinating truths about the brain’s incredible plasticity and the competitive nature of its language networks.

What Exactly Is First Language Attrition?

First language (L1) attrition is the gradual, non-pathological decline in proficiency in a native language. It’s crucial to distinguish this from language loss caused by brain damage, disease, or aging (like aphasia). Attrition is a direct consequence of acquiring and becoming dominant in a second language (L2), typically through prolonged immersion in a new country or linguistic environment.

It’s not about “forgetting” your language entirely. Very few people, unless they left their home country at a very young age, will ever completely lose their L1. Instead, attrition is a spectrum. It can manifest as minor hesitations and word-finding difficulties, or in more advanced cases, it can affect grammar and even accent.

The Telltale Signs: How Attrition Shows Up

L1 attrition isn’t uniform; it chips away at different parts of language at different rates. The effects are most commonly seen in the following areas:

Lexical Access (Vocabulary)

This is usually the first and most noticeable casualty. It includes:

• Slower word retrieval: The classic “tip-of-the-tongue” state becomes more frequent. The word is still stored in your memory, but accessing it takes longer.
• Code-switching and borrowing: You might unintentionally pepper your L1 speech with L2 words, especially for concepts you primarily discuss in your L2 (like work terminology).
• Calques: This is a more subtle form of borrowing where you translate an L2 expression literally into your L1, creating a phrase that sounds unnatural to other native speakers. For example, a native German speaker living in the U.S. might say “Ich nehme eine Dusche” (literally “I take a shower,” copying the English phrase) instead of the more natural German “Ich dusche” (“I shower”).

Phonology (The Sound System)

While your core accent often remains, subtle shifts can occur. The phonological system of your dominant L2 can start to “bleed” into your L1. A native Russian speaker might, after decades in an English-speaking country, start pronouncing the Russian ‘r’ with a slightly less pronounced roll, closer to its English counterpart. These changes are often so minor that only a trained linguist—or a critical relative—would notice.

Syntax and Grammar

Grammar is generally more resilient than vocabulary, but it’s not immune. Long-term attriters might begin to simplify complex grammatical structures in their native tongue or, in some cases, incorrectly apply L2 grammar rules. For instance, a native English speaker who becomes fluent in French might be tempted to place adjectives after the noun in English, a pattern that is standard in French but rare in English.

The “Why”: Competition and Inhibition in the Brain

So, why does this happen? The answer lies not in a failure of memory, but in the way a multilingual brain manages its resources. The old idea of languages being stored in separate, neat boxes in the brain has been thoroughly debunked. Instead, modern neuroscience paints a picture of a dynamic and integrated network.

The leading theory is the Activation Threshold Hypothesis. Think of every word and grammatical rule in your brain as having a baseline level of activation. The more you use a language, the higher its activation level, meaning its components are easier and faster to access. When you move to a new country and use your L2 for everything—work, shopping, socializing—the L2’s activation level skyrockets. Simultaneously, your L1, through disuse, sees its activation level drop. It’s not gone; it’s just become harder to “fire up.” The brain, being ruthlessly efficient, prioritizes the language it needs most.

This is tied to the concept of inhibition. When a multilingual person speaks, both (or all) of their languages are technically active at the same time. To speak just one, the brain must actively suppress, or inhibit, the other(s). Over time, if you are constantly using your L2, your brain becomes incredibly good at inhibiting your L1. Attrition is the side-effect of this highly effective inhibition mechanism. You’re not forgetting your mother tongue; your brain has just become too good at sidelining it.

Factors That Influence Attrition

Not everyone experiences attrition to the same degree. Several factors play a role:

• Age: The younger you are when you immerse yourself in an L2 environment, the more profound the attrition of your L1 is likely to be.
• Motivation and Identity: Individuals who strongly associate their L1 with their personal identity and are motivated to maintain it tend to show less attrition.
• Exposure: This is the big one. How often do you use your L1? Do you have family to speak with? Do you read books or watch movies in your native language? The more you use it, the more you keep it.

Can You Fight It? Reawakening a Dormant Language

The good news is that because the language isn’t truly gone, it can be reawakened. L1 attrition is largely reversible. The knowledge is latent, waiting to be reactivated.

Re-engaging with the language is the key. This can involve:

• Making a conscious effort to speak your L1 with family and friends.
• Consuming media: watching films, listening to music or podcasts, and reading books in your native tongue.
• Visiting your home country, if possible, provides a powerful immersive boost.

Many people report that after a brief period of re-immersion, their language skills come flooding back, feeling more natural and fluid than they have in years.

Ultimately, first language attrition is not a personal failing but a testament to the brain’s remarkable ability to adapt to its environment. It’s a living example of neuroplasticity—the “use it or lose it” principle in action. It reminds us that language is not a static object we possess, but a dynamic skill we must continually cultivate. So the next time you stumble for a word in your mother tongue, don’t despair. Instead, marvel at the complex, competitive, and constantly shifting linguistic dance happening inside your own mind.