COVID-19 Links Loss of Smell to Long-Term Brain Changes, Cognitive Disturbances

COVID-19 Links Loss of Smell to Long-Term Brain Changes, Cognitive Disturbances
COVID-19 Links Loss of Smell to Long-Term Brain Changes, Cognitive Disturbances

United States: A groundbreaking study, recently unveiled in Scientific Reports, has illuminated the enduring neurological ramifications stemming from COVID-19. The researchers discerned that individuals afflicted by anosmia— the abrupt loss of olfactory function— during their bout with COVID-19 demonstrated measurable alterations in both brain functionality and its physical architecture throughout recovery.

This pioneering research is among the first to establish a direct correlation between COVID-19-related anosmia and tangible changes in cerebral architecture, according to the reports by psypost.org.

COVID-19, triggered by the SARS-CoV-2 virus, has predominantly been recognized for its impact on the respiratory system. However, with the passage of time, numerous patients, even those who experienced mild symptoms, have reported cognitive disturbances such as memory impairment, confusion, and concentration difficulties. These observations have raised alarm regarding the virus’s potential impact on the brain. Symptoms such as headaches, cognitive haze, and anosmia emerged as commonplace among COVID-19 survivors.

Anosmia, which denotes the loss of olfactory perception, quickly became one of the most prominent and abrupt indicators of COVID-19. While many individuals regained their olfactory function within a matter of weeks, others experienced prolonged dysfunction. Previous investigations suggested that a loss of smell might foreshadow more extensive neurological implications in afflictions such as Alzheimer’s and Parkinson’s diseases. Given the prevalence of anosmia in COVID-19 cases and its potential ramifications on brain health, researchers sought to examine whether anosmia during COVID-19 was linked to discernible cerebral modifications in those recovering from the virus.

“Our laboratory is dedicated to unearthing the neurobiological mechanisms underpinning complex social behaviors and decision-making processes. The pandemic severely hampered our experimental endeavors due to health restrictions,” remarked study co-author Pablo Billeke of the Center for Research in Social Complexity at the University for Development in Chile.

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“In light of the early accounts of neurological manifestations in patients struck by COVID-19, we were compelled to offer insights from our distinctive vantage point. We aimed to decipher the potential neural damage wrought by SARS-CoV-2 infections, prompting us to initiate this study. We scrutinized recovered COVID-19 patients through structural and functional MRI scans, which were conducted while participants engaged in tasks involving decision-making and cognitive control. We also monitored their neurological evolution via electroencephalography (EEG),” Billeke elaborated.

In pursuit of these objectives, the researchers enlisted 100 adults in Santiago, Chile, who had recuperated from respiratory infections between February 2020 and May 2023. The final cohort included 73 participants with confirmed COVID-19 infections, while the remaining subjects had suffered from respiratory illnesses induced by other pathogens, as confirmed by multiple negative PCR tests. The researchers employed a range of assessments, including brain scans, to evaluate both the functionality and structure of the participants’ brains across two separate sessions, as per psypost.org.

The age range of participants spanned from 19 to 65 years old, none of whom had required ventilatory support or intensive care. Notably, individuals with pre-existing neuropsychiatric disorders or significant brain injuries were excluded to ensure that the effects observed could be attributed to the COVID-19 infection rather than prior conditions.

In behavioral assessments, individuals with a history of anosmia exhibited more impulsive decision-making behaviors compared to those who retained their olfactory capabilities. Specifically, these individuals demonstrated a heightened tendency to alter their choices following negative feedback, particularly during tasks that required adaptation to shifting probabilities of rewards. Though this impulsivity resulted in greater gains in decision-making tasks involving rapidly fluctuating conditions, it underscored an alteration in the way their brains processed risks and rewards.

From a functional perspective, patients with a history of anosmia exhibited diminished brain activity during decision-making tasks in regions critical for evaluating choices, particularly the lateral prefrontal cortex, and temporoparietal junctions.

Structurally, brain imaging revealed that participants with anosmia had a pronounced thinning of specific brain regions. These changes were most prominent in the parietal lobes, which are vital for processing sensory information and spatial awareness. This thinning could signify long-term structural transformations in the brain linked to the virus in those who experienced olfactory loss.

Furthermore, these individuals showed diminished white matter integrity, especially in the tracts connecting vital brain regions. White matter plays an indispensable role in facilitating inter-regional communication within the brain, and disruptions in these pathways could lead to various cognitive impairments.

“In today’s context, where a substantial proportion of the global population has contracted COVID-19 at some point, it becomes imperative to pinpoint factors that may predispose certain individuals to cerebral alterations post-infection,” Billeke explained to PsyPost. “Our study discovered that individuals who experienced anosmia during the acute phase of infection exhibited discernible changes in brain structure and demonstrated distinct patterns in decision-making tasks that involved learning.”

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“Notably, these individuals displayed more impulsive decisions when the environmental context shifted. Although these changes might not necessarily lead to long-term consequences, they could serve as early markers to monitor individuals who suffer from anosmia. This might help determine whether such individuals are more vulnerable to developing neurodegenerative diseases. This is especially relevant when other risk factors, such as cardiovascular ailments, diabetes, or genetic predispositions, are present, all of which are associated with the onset of neurodegenerative conditions,” according to the reports.

Interestingly, the study found that these brain changes were less pronounced in individuals with more severe respiratory symptoms, including those requiring hospitalization. This suggests that anosmia may serve as a more reliable indicator of neurological involvement than the severity of respiratory symptoms, as per psypost.org.

“What struck us most was the consistency of findings in patients with anosmia, irrespective of the severity of their respiratory symptoms,” Billeke noted, adding, “These individuals displayed measurable alterations in both behavioral tests and brain function and structure, impacting both white matter and gray matter.”

Although the study provides vital insights, there are notable limitations. Primarily, it relied on self-reported anosmia symptoms, corroborated by the KOR test— a validated tool for detecting olfactory deficits linked to COVID-19. More robust, objective clinical assessments would strengthen the evidence.

Moreover, the study lacked baseline brain scans predating the participants’ COVID-19 infections, making it challenging to establish a direct causal link between the virus and the findings. “Nonetheless, when juxtaposed with the growing body of literature from other studies utilizing extensive databases, we can confidently assert that the virus triggers neural alterations,” Billeke explained. “While the exact mechanisms remain elusive, the correlations we observed are consistent with other evidence pointing toward a causal relationship between SARS-CoV-2 infection and the observed neural damage.”

Looking ahead, the research team plans to track these participants longitudinally to determine whether the observed brain changes endure or impact their daily functioning. The team also aims to explore potential therapeutic avenues, such as brain stimulation techniques, to alleviate lingering neurological and cognitive effects in post-COVID-19 patients.

“Our ongoing electroencephalography (EEG) studies are focused on identifying the oscillatory patterns associated with these neural alterations,” Billeke added. “We hope that pinpointing these patterns will lead to the development of brain stimulation therapies— such as transcranial electrical or magnetic stimulation— to mitigate the enduring symptoms,” according to the reports by psypost.org.

Billeke concluded by expressing profound gratitude to the study’s participants for their dedication, particularly during the challenges posed by pandemic-related restrictions, and to the research team for their tireless efforts.

The study, titled “Patients recovering from COVID-19 who presented with anosmia during their acute episode have behavioral, functional, and structural brain alterations,” was conducted by Leonie Kausel, Alejandra Figueroa-Vargas, Francisco Zamorano, and their colleagues.