Nonverbal memory tests revisited: Neuroanatomical correlates and differential influence of biasing cognitive functions

The detection of right temporal lobe dysfunction with nonverbal memory tests has
remained difficult in the past. Reasons for this might be the potential influence of other
biasing cognitive functions such as executive functions or the verbalisability of nonverbal
material. The aim of this study was to investigate three classic nonverbal memory tests by
identifying their neuroanatomical correlates with lesion-symptom mapping (LSM) and by
probing their independence from verbal encoding abilities and executive functions.
In a cohort of 119 patients with first-time cerebrovascular accident, memory perfor-
mance was assessed in the Nonverbal Learning and Memory Test for Routes (NLMTR), the
Rey Complex Figure Test (RCFT), and the Visual Design Learning Test (VDLT). Calculating
multivariate LSM, we identified crucial brain structures for these three nonverbal memory
tests. Behavioural analyses were performed to assess the impact of executive functions
and verbal encoding abilities with regression analyses and likelihood-ratio tests.
LSM revealed for the RCFT mainly right-hemispheric frontal, insular, subcortical, and
white matter structures and for the NLMTR right-hemispheric temporal (hippocampus),
insular, subcortical, and white matter structures. The VDLT did not reach significance in
LSM analyses. Behavioural results showed that amongst the three nonverbal memory tests
the impact of executive functions was most pronounced for RCFT, and the impact of verbal
encoding abilities was most important in VDLT. Likelihood-ratio tests confirmed that only
for NLMTR did the goodness of fit not significantly improve by adding executive functions
or verbal encoding abilities.
These results suggest that amongst the three nonverbal memory tests the NLMTR, as a
spatial navigation test, could serve as the most suitable marker of right-hemispheric
temporal lobe functioning, with the right hippocampus being involved only in this test.