A reason has been discovered for why individuals with aphasia lose the ability to speak about the past and future.

The research findings have been published in the journal Aphasiology. Aphasia is a severe speech disorder that often occurs after a stroke, where an individual loses the ability to speak coherently. This can manifest in incorrect usage of verb tenses, making it difficult for the person to talk about events in the past or future. Such issues can lead to significant problems in everyday communication.

Scientists from universities in Russia, Greece, Italy, the USA, and Norway conducted an experiment to understand why these difficulties arise. The researchers hypothesized that the difficulties in expressing temporal categories could be linked to two different processes: coding and retrieval. During coding, the speaker forms an idea of time: whether the action is happening in the past, present, or future.

In the retrieval process, the individual selects the correct form of the word for the given temporal indication. To determine how each of these processes affects speech, the scientists conducted an experiment involving individuals with aphasia who spoke four different languages: Greek, Russian, Italian, and English. These languages were chosen deliberately, as the verb forms related to time are structured differently in each. This allows for an examination of how language features influence the coding and retrieval of temporal forms in patients with aphasia.

For diagnostics, the researchers developed two tasks for sentence completion. In the first task, participants were asked to fill in the blanks in sentences, requiring the use of both processes—coding and retrieval. Participants had to complete a sentence based on a model, considering changes in the verb tense. For example: “Yesterday the gardener watered the flowers. Tomorrow the gardener… flowers.” In the second task, they needed to complete the sentence without altering the verb tense. The participant saw the phrase “water the plants” and heard the model “the gardener is currently picking mushrooms.” They were then asked to start the sentence “the gardener is currently…,” which needed to be completed with the phrase “watering the plants” in the correct form, that is, “is watering the plants.”

By comparing the results of each of these tasks, the researchers were able to identify at which stage—coding or retrieval—the participants faced the most significant challenges.

It was found that most participants exhibited difficulties in both coding and retrieval of verb tenses, but the severity of these difficulties varied by language and individual. For instance, Russian and English speakers often struggled more with the retrieval task, while some Greek and Italian speakers encountered challenges at the coding stage. Interestingly, the difficulties in temporal expression manifested selectively: some patients had more trouble indicating the past tense, while others struggled with the future tense.

“These results are particularly important for understanding that patients with aphasia can lose their ability to express time differently depending on the features of the language they speak,” explains one of the authors of the article, researcher Olga Buivolova from the HSE Center for Language and Brain. “Now we can more accurately assess which aspects of time pose the greatest challenges for patients and begin developing more personalized therapeutic approaches.”

As the researchers note, the main conclusions of the study may also have practical implications for neurorehabilitation. First, this experimental method can help identify the underlying causes of difficulties with the use of verb tenses. This means that speech therapists and neuropsychologists will be able to work more thoroughly and effectively with patients on speech recovery.

Second, the study aids in understanding how differences between languages can influence the symptoms of aphasia. This is important for creating standardized tests and methodologies that take into account the specifics of the speaker's native language, ultimately leading to more accurate and comprehensive diagnostics for patients with aphasia.