Table 3.

Summary of study procedures and findings of included case studies and case series.

Included studies	Modalities	Study procedures and main findings
Allen and Absar, 2022*	PET and Structural MRI	A 79-year-old female patient without significant past medical history complained mild short-term memory loss over several years likely due to aging. This memory impairment did not interfere with her daily life until her confirmed diagnosis of COVID-19, which severely worsened her dementia especially episodic memory and word finding difficulties over 10 months following COVID-19 infection. No abnormalities were seen on her brain MRI. PET scan exhibited obvious hypometabolism in the left temporal lobe and mild hypometabolism in the adjacent left frontal and parietal regions.
Branco de Oliveira et al., 2021*	PET and Structural MRI and EEG	A 47-year-old female patient experienced persistent short-term memory problems during COVID infection. Brain MRI and EEG exams showed no abnormalities. Her memory impairment improved after 2 days of treatment during hospitalization. Complaint about discrete memory still existed after 20 days from discharge, though it did not interfere with her daily life activity.
Das et al., 2022*	Structural MRI and EEG	Cognitive function assessment noted impairment of recent memory in a 33-year-old male patient with no significant past medical or psychiatric history following COVID infection. Brain MRI scan showed few tiny and non-specific hyperintense foci in bilateral frontal subcortical and left parietal periventricular white matter. EEG showed intermittent diffuse slow waves with atypical triphasic waves suggestive of diffuse dysfunction of brain.
Garg et al., 2020*	CT and Structural MRI	A 59-year-old female patient complained about memory deficits (difficulty remembering daily schedules and names) after initial COVID infection. When her memory impairments acutely worsened 2 months after COVID infection, she was found to have a chronic ischemic stroke. CT and MRI of the head were carried out during an emergency admission 2 months after her initial viral infection. Non-contrast CT suggested hypodensity in the left frontal lobe, while MRI with contrast indicated hyperintense signal abnormalities in the left frontal lobe.
Hugon et al., 2022a**	PET and Structural MRI	Fluorodeoxyglucose PET was performed in three COVID-19 patients with cognitive complaints, especially with memory problems as shown in the complete neuropsychological examinations. Brain MRIs were normal in all three patients. The hypometabolic pons was observed in these patients, as revealed by the cerebral FDG PET.
Hugon et al., 2022b**	PET	Cerebral FDG PET showed significant brainstem hypometabolism, especially in the pons in three COVID-19 patients with memory impairments.
Jacobs et al., 2021*	MRI and CT	A 55-year-old male patient with COVID-19 suffered memory impairment. Brain CT showed hypodense ischemic plaques extending from the lentiform nucleus to the anterior horn of the left lateral ventricle. MRI scan showed zones with diffusion restriction in the bilateral corona radiata extending up to the semioval regions.
Matias-Guiu et al., 2021*	PET and Structural MRI	A 67-year-old female patient without past medical or psychiatry history developed obvious memory problems 6 months after the onset of COVID-19. One month later, the neuropsychological assessments suggested verbal episodic memory deficits. MRI and PET showed no abnormalities on visual analysis, but semi-quantitative analysis of meta-region of interest (meta-ROI) of FDG-PET indicated hypometabolism in regions associated with Alzheimer's Disease (such as the hippocampal region).
Morand et al., 2022**	PET	[18F]-FDG PET metabolism of seven pediatric patients with suspected long-COVID was evaluated in comparison to 21 pediatric controls, and of 35 adult patients with long COVID in comparison to 44 healthy adult controls. It was found that the seven pediatric patients experienced memory difficulties for more than 4 weeks following the initial acute COVID-19 phase, without symptom-free interval. After an average of 5 months, pediatric patients showed a pattern of brain hypometabolism similar to that seen in adults with long-COVID, involving bilateral medial temporal lobes (such as amygdala and parahippocampal gyrus), brainstem, and cerebellum (p-voxel < 0.001, p-cluster < 0.05 FWE-corrected).
Polascik et al., 2021**	Structural MRI and CT	Three adult patients over age 65 complained significantly worsened memory difficulties after COVID-19 infection. Non-contrast head CT before COVID-19 infection showed mild bilateral hippocampal atrophy in patient 1; MRI in patient 2 revealed mild hippocampal and biparietal lobe atrophy as well as mild cerebral white matter disease; non-contrast head CT performed 3 weeks after COVID-19 diagnosis showed calcification in the right basal ganglia and a mild hypodense signal periventricularly in patient 3. Noncontrast brain MRI showed subtle hippocampal and perisylvian atrophy and mild to moderate parietal lobe atrophy bilaterally.
Ravaglia et al., 2021*	MRI	A 58-year-old female patient without any past medical condition experienced transient global amnesia (TGA), spatial memory in particular, 1 h after executing first-time PCR viral swab test for COVID-19 (later revealing as negative). MRI was performed 1 day after TGA. DWI image suggested a typical punctate focus restriction in her right hippocampus. However, the swab-induced physical or psychological stimulation was believed the trigger of causing her hippocampal abnormality.
Savino et al., 2022**	Structural MRI, EEG and CT	Five patients under 18 years of age were admitted due to new-onset neuropsychiatric symptoms. In case 1, a 15-year-old male patient suffered recent memory impairment in the absence of gross cognitive decline. Brain CT, EEG and MRI showed no significant abnormalities, except for a slight descent of the right cerebellar tonsil and a thinning corpus callosum. Both EEG and MRI were normal in other four cases, who did not report memory problems.
Terruzzi et al., 2022*	Structural MRI, PET and EEG	A 51-year-old female patient complained episodic and prospective memory problems, which were confirmed via neuropsychological examination. EEG results were normal, but MRI scan showed hyperintensity of signal in the paracallosal and periventricular white matter. The 18F-FDG PET-CT brain scan following her hospital discharge showed cortical hypometabolism, except for the occipital lobes.
Vandervorst et al., 2020*	Structural MRI and CT	Cognitive testing revealed immediate and short-term memory deficits in a 29-year-old male patient with no prior medical history 2 weeks after the onset of COVID-19 symptoms CT scan was normal, while the first MRI scan showed an asymmetric FLAIR (fluid-attenuated inversion recovery) hyperintensity in the left medial temporal cortex associated with mild gyral expansion. During his hospitalization, a second brain MRI scan, 4 days after the first MRI, showed normalization of cortical hyperintensity and gyral expansion; meanwhile, his memory difficulties improved.
Yesilkaya et al., 2021*	Structural EEG, CT, and MRI and MRS	A 29-year-old male patient developed memory impairment, such as difficulty recalling past experiences 2 weeks after the completion of treatment for COVID-19. FAB was used to evaluate frontal lobe dysfunction and GDS was used to stage cognitive decline. The FAB score was 13 and the GDS stage was 3 initially, indicating mild memory decline. No memory deficit was detected after 3 months. Structural neuroimaging results through EEG, CT and MRI were normal in his initial screening. MRS of the bilateral DLPFC 1 week after COVID infection revealed significantly decreased levels of N-acetylaspartate (166,65), glutamate (31,54), and glutamate/glutamine ratio (0,13). Three months later, a repeat MRS of DLPFC suggested significantly improved levels of N-acetylaspartate (183,14), while levels of the other two metabolites did not improve compared to the first MRS.

CT, Computed Tomography; DLPFC, dorsolateral prefrontal cortex; DTI, Diffusion Tensor Imaging; EEG, electroencephalogram; FAB, Frontal Assessment Battery; FDG, fluorodeoxyglucose; GDS, Global Deterioration Scale; GMV, Gray Matter Volume; MRI, Magnetic Resonance Imaging; MRS, MR-spectroscopy; PET, Positron Emission Tomography.

^*Case study.

^**Case series.