New Delhi, April 5 : Infection with SARS-CoV-2 has a significant impact on cognitive function in patients with preexisting dementia, according to new research led by health experts from West Bengal. Since the first wave of Covid-19, neurologists have noticed both acute and long-term neurological impact of this infectious disease. While insights Covid's effect on human cognition has remained unclear, neurologists have often referred to it as "brain fog" -- an ambiguous terminology. To better describe the cognitive effects, the team proposed a new term: 'FADE-IN MEMORY' (that is, fatigue, decreased fluency, attention deficit, depression, executive dysfunction, slowed information processing speed, and subcortical memory impairment)." They investigated the effects of Covid-19 on cognitive impairment in 14 patients with preexisting dementia (four with Alzheimer's, five with vascular dementia, three with Parkinson's, and two with the behavioural variant of frontotemporal dementia), who had suffered further cognitive deterioration following Covid-19. The results, published in the Journal of Alzheimer's Disease Reports, showed that patients with all subtypes of dementia experienced rapidly progressive dementia following infection with SARS-CoV-2. "As the ageing population and dementia are increasing globally, we believe pattern recognition of Covid-19-associated cognitive deficits is urgently needed to distinguish between Covid-19-associated cognitive impairments per se and other types of dementia," said Dr. Souvik Dubey, from the Department of Neuromedicine, at Bangur Institute of Neurosciences (BIN), Kolkata. "This understanding will have a definitive impact on future dementia research," he added. In addition, the team found that irrespective of patients' previous dementia types, the line of demarcation between different types of dementia became remarkably blurry post-Covid. Researchers also found that the characteristics of a particular type of dementia changed following Covid-19, and both degenerative and vascular dementia started behaving like mixed dementia both clinically and radiologically. A rapidly and aggressively deteriorating course was observed in patients having insidious onset, slowly progressive dementia, and who were previously cognitively stable. The rapid progression of dementia, the addition of further impairments/deterioration of cognitive abilities, and the increase or new appearance of white matter lesions suggest that previously compromised brains have little defence to withstand a new onslaught (that is, a "second hit" like infection/dysregulated immune response and inflammation), they explained. /IANS