Abstract
HIGHLIGHTS Memory correlates with the difference between single and double-sensory evoked steady-state coherence in the gamma range (ΔC).The correlation is most pronounced for the anterior brain region (ΔCA).The correlation is not driven by birth size, education, speed of processing, or intelligence.The sensitivity of ΔCA for detecting low memory capacity is 90%.Cerebral rhythmic activity and oscillations are important pathways of communication between cortical cell assemblies and may be key factors in memory. We asked whether memory performance is related to gamma coherence in a non-task sensory steady-state stimulation. We investigated 40 healthy males born in 1953 who were part of a Danish birth cohort study. Coherence was measured in the gamma range in response to a single-sensory visual stimulation (36 Hz) and a double-sensory combined audiovisual stimulation (auditive: 40 Hz; visual: 36 Hz). The individual difference in coherence (ΔC) between the bimodal and monomodal stimulation was calculated for each subject and used as the main explanatory variable. ΔC in total brain were significantly negatively correlated with long-term verbal recall. This correlation was pronounced for the anterior region. In addition, the correlation between ΔC and long-term memory was robust when controlling for working memory, as well as a wide range of potentially confounding factors, including intelligence, length of education, speed of processing, visual attention and executive function. Moreover, we found that the difference in anterior coherence (ΔCA) is a better predictor of memory than power in multivariate models. The sensitivity of ΔCA for detecting low memory capacity is 92%. Finally, ΔCA was also associated with other types of memory: verbal learning, visual recognition, and spatial memory, and these additional correlations were also robust enough to control for a range of potentially confounding factors. Thus, the ΔC is a predictor of memory performance may be useful in cognitive neuropsychological testing.
Highlights
The aim of the present study was to investigate whether memory is associated with functional brain connectivity, whether measures of memory function correlate with neurophysiological gamma band coherence, using a novel two-sense stimulation method involving passive nontask monomodal and combined bimodal stimulation
As processes that modulate the occipital gamma activity reside in the frontal cortex (Knight et al, 1999; Barceló et al, 2000; Herrmann et al, 2004a,b; Muthukumaraswamy et al, 2010) and because some studies tend to find that prefrontal activity is related to memory performance we focused on both the total coherence and the anterior coherence
Right, Intra, and Inter-Hemispheric Differences Subdividing the differences in total coherence into right and left hemispheric coherence, we found that the coherence at the language-specific left hemisphere significantly negatively correlated with long-term memory with higher explanatory power than the right side, and significant on 10% level in the anterior part of the brain
Summary
The aim of the present study was to investigate whether memory is associated with functional brain connectivity, whether measures of memory function correlate with neurophysiological gamma band coherence, using a novel two-sense stimulation method involving passive nontask monomodal and combined bimodal stimulation. Our study provides evidence that the difference in electrophysiological connectivity between singlesensory and double-sensory stimulation is associated with longterm memory, accounting for a wide range of unobserved and observed potentially confounding factors. One starting point is the observation that communication between different brain regions provides the basis for the integration of, for example, sensory information and sensory-motor coordination, which are critical for information processing, learning, and memory (Herrmann et al, 2004a). For this reason alone, one may hypothesize that differences in brain connectivity between individuals may explain differences in memory performance. Consistent with this notion, the so-called Hebbian theory hypothesize how neurons connect to become engrams and bind together and store memory traces (Morris, 1999)
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