Spatial navigational strategies correlate with gray matter in the hippocampus of healthy older adults tested in a virtual maze

Abstract

Healthy young adults use different strategies when navigating in a virtual maze. Spatial strategies involve using environmental landmarks while response strategies involve executing a series of movements from specific stimuli. Neuroimaging studies previously confirmed that people who use spatial strategies show increased activity and gray matter in the hippocampus, while those who use response strategies show increased activity and gray matter in caudate nucleus (Iaria et al., 2003; Bohbot et al., 2007). A growing number of studies report that cognitive decline that occurs with normal aging is correlated with a decrease in volume of the hippocampus. Here, we used voxel-based morphometry (VBM) to examine whether spatial strategies in aging are correlated with greater gray matter in the hippocampus, as found in our previous study with healthy young participants. Forty-five healthy older adults were tested on a virtual navigation task that allows spatial and response strategies. All participants learn the task to criterion after which a special "probe" trial that assesses spatial and response strategies is given. Results show that spontaneous spatial memory strategies, and not performance on the navigation task, positively correlate with gray matter in the hippocampus. Since numerous studies have shown that a decrease in the volume of the hippocampus correlates with cognitive deficits during normal aging and increases the risks of ensuing dementia, the current results suggest that older people who use their spatial memory strategies in their everyday lives may have increased gray matter in the hippocampus and enhance their probability of healthy and successful aging.

Keywords: aging; hippocampus; navigation; radial maze; spatial memory.

Figure 1

The two stages of the virtual radial maze with a schematic representation of the behavioral paradigm. Example of a pair of arms presented during encoding (Stage 1) and a recombined pair during Stage 2.

Figure 2

Whole brain regression analysis with scores on recombined pairs condition of CSDLT (Stage 2). Results are superimposed onto an anatomical MRI and displayed in the sagittal plane. Results show that gray matter in the hippocampus significantly co-vary with spatial navigational strategies (MNI space coordinates x = 26.0, y = −37.8, z = −3.2; t = 3.53, p < 0.0005).

Figure 3

Correlation between scores on the recombined pairs condition (Stage 2) of the CSDLT and gray matter values extracted from the peak voxel (MNI space coordinates x = 26.0, y = −37.8, z = −3.2) in the right posterior hippocampus (r = 0.478, p < 0.001). This graph shows that a better spatial memory score is associated with increased gray matter in the hippocampus.

Figure 4

Regions of the brain that co-varied with our peak hippocampal gray matter value (x = 26.0, y = −37.8, z = −3.2). A, Amygdala; HPC, hippocampus; PHC, parahippocampal cortex; OFC, orbitofrontal cortex. The color bar illustrates the range of t statistical values.