Using Virtual Reality to Detect Early Alzheimer's Disease

What percentage of layer II entorhinal cortex (EC) neurons is lost by the time cognitive impairment becomes manifest in Alzheimer's disease?

Approximately 60% of layer II EC neurons are lost by the time cognitive impairment is clinically manifest.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

Why is the medial entorhinal cortex (mEC) considered more heavily involved in navigation compared to the lateral entorhinal cortex?

Up to 95% of mEC neurons may be grid cells, whereas lateral entorhinal cortex neurons exhibit very little spatial selectivity.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

What are the human homologues of the rodent medial and lateral entorhinal cortex subdivisions?

The rodent lateral EC is homologous to the human anterolateral EC (alEC), and the rodent medial EC is homologous to the human posteromedial EC (pmEC).

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

How do the spatial representation roles of the human anterolateral EC (alEC) and posteromedial EC (pmEC) differ?

The alEC represents sensory characteristics of objects, whereas the pmEC represents scenes and current location based on self-motion cues.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

What is path integration and what sensory inputs does it depend on?

Path integration is the ability to track and return to a previously visited location, and it depends on integrating visual, proprioceptive, and vestibular cues.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

What is the Four Mountains Test (4MT) and what does it measure?

The 4MT is a hippocampal-dependent test of allocentric spatial memory used to differentiate MCI patients and predict dementia conversion.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

Why does immersive virtual reality (iVR) have theoretical advantages over desktop VR tasks for evaluating grid cell function?

Immersive VR provides motor and proprioceptive feedback from physical walking, which is essential for grid cell function but absent in desktop VR tasks.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

How do hippocampal theta oscillations differ between desktop virtual reality and active navigation?

Desktop VR navigation is associated with lower frequency hippocampal theta oscillations than actual, physical navigation.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

What spatial errors are typically larger in desktop virtual reality compared to active-movement tasks?

Desktop VR navigation tends to yield larger rotational and distance errors due to the lack of self-motion feedback.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

What are the five requirements for a clinical diagnosis of Mild Cognitive Impairment (MCI) according to the Petersen criteria?

Diagnosis requires: (1) subjective cognitive complaint, (2) objective cognitive impairment, (3) preserved daily living activities, (4) functional independence, and (5) absence of dementia.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

What CSF biomarker thresholds were used in this study to classify patients as MCI biomarker-positive (MCI+)?

The thresholds were CSF amyloid-beta < 550 pg/ml, CSF total tau > 375 pg/ml, and a CSF tau to amyloid-beta ratio > 0.8.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

Why did the researchers design the virtual reality environments without local landmark cues?

Excluding local landmarks forced participants to rely on entorhinal-grid cell path integration strategies instead of striatal-mediated landmark strategies.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

What physical layout did participants navigate during the outward phase of the VR path integration task?

Participants walked an "L"-shaped outward path to three locations marked by virtual cones.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

What three environmental return conditions were used during the VR path integration task?

The three conditions were Condition A (no change), Condition B (removal of boundary cues), and Condition C (removal of surface details).

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

What was the theoretical purpose of removing boundary cues in Return Condition B?

It aimed to increase dependency on self-motion cues and homing vector calculations, increasing cognitive load on the path integration network.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

How did Return Condition C (removal of surface details) stress the navigation system?

It prevented visual feedback from surface motion, disrupting optic flow and forcing dependence on allocentric representations of space.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

How was the primary outcome measure, absolute distance error, calculated?

It was defined as the Euclidean distance between the participant's estimated return location and the actual starting location of cone 1.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

What two secondary outcome measures deconstructed the absolute distance error?

The two secondary outcome measures were proportional angular error and proportional linear error.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

How were high-resolution T2-weighted MRI scans aligned when scanning the hippocampal formation?

The high-resolution T2-weighted scans were aligned orthogonally to the long axis of the hippocampus.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

How did the researchers partially segment the alEC and pmEC subregions on 3T MRI?

They utilized an in-house protocol that segmented the three anterior-most and three posterior-most slices of the EC, skipping intermediate slices.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

Why were the intermediate entorhinal cortex slices excluded from subregion segmentation in this study?

Intermediate slices were omitted because of the spatial overlap between alEC and pmEC and the lack of clear landmarks to delineate their boundary on 3T MRI.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

What proxies were used for the retrosplenial cortex in Freesurfer segmentations?

The posterior cingulate cortex (PCC) and the isthmus of the cingulate cortex were used as proxies for the retrosplenial cortex.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI

Approximately what percentage of the virtual reality navigation trials were excluded, and what was the main cause?

About 33.77% of trials were excluded because participants hit the physical 'out of border' boundary.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

How did the absolute distance error of the combined MCI group compare to that of healthy controls?

The combined MCI group exhibited significantly larger errors, showing an estimated 57 cm increase in absolute distance error compared to controls.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

How did biomarker-positive MCI (MCI+) patients compare to biomarker-negative MCI (MCI-) patients in absolute distance error?

MCI+ patients had significantly larger absolute distance errors, with an estimated increase of about 98 cm compared to MCI- patients.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

How did global cognitive scores (ACE-R) relate to performance on the VR path integration task?

Lower ACE-R scores significantly correlated with larger absolute distance errors in both control/MCI and MCI+/MCI- comparisons.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

Which CSF biomarkers were predictive of absolute distance error in the path integration task, and in what directions?

Absolute distance error correlated positively with CSF total tau and negatively with CSF amyloid-beta.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

Which specific path integration error component—linear or angular—differentiated the diagnostic groups in this study?

Proportional linear errors (distance estimation) successfully differentiated the diagnostic groups, whereas proportional angular errors did not show significant group differences.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

What was the effect of changing the environmental return conditions (no change vs. no boundary vs. no surface detail) on absolute distance error?

There was no significant main effect or interaction effect of the return conditions on absolute distance error for any of the groups.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

Which brain regions showed a significant negative association with absolute distance error that survived multiple comparison correction?

The total entorhinal cortex (EC) and posteromedial EC (pmEC) volumes showed significant negative associations with absolute distance error.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

Did total EC and pmEC volumes remain significant predictors of absolute distance error when controlling for hippocampal and alEC volumes?

Yes, both total EC and pmEC volumes were significant predictors in these models, though they did not survive multiple comparison corrections.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

Were hippocampal or pmEC volumes significant predictors of performance on the Four Mountains Test (4MT)?

No, neither hippocampal nor pmEC volumes significantly predicted performance on the Four Mountains Test across all participants.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

How accurately did absolute distance error differentiate total MCI patients from healthy controls?

It differentiated them with an AUC of 0.82, with a threshold of 157 cm or greater yielding 84% sensitivity and 68% specificity.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

What was the classification accuracy (AUC) of the absolute distance error for differentiating MCI+ from MCI- patients?

The task achieved a high AUC of 0.90, where an error threshold of 196 cm or greater yielded both sensitivity and specificity of 92%.

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI · quote verified

How did the VR task's ability to differentiate MCI+ from MCI- compare to standard cognitive tests?

The VR task was markedly superior (AUC = 0.90), while traditional tests like the ACE-R and 4MT performed close to chance level (AUCs of 0.53 to 0.57).

Source: Differentiation of mild cognitive impairment using an entorhinal cortex-based test of virtual reality navigation · DOI