Lateralisation and localisation of spatial and verbal associative recognition memory

Episodic memory is the conscious recalling of past experiences. The neural underpinnings of this skill have long been of clinical interest, as deficits can be debilitating, including to those with temporal lobe pathology. This study sought to improve the assessment of those with unilateral temporal lobe pathology by comparing the localisation and lateralisation of successful spatial and verbal associative recognition memory using 3D time-frequency analysis and connectivity analysis of EEG data, while reducing perceptual confounds. Twenty right-handed participants aged 18 to 33 years were included. Average band-power analysis in eLORETA was used to compare verbal associative memory, spatial associative memory, and the resting state to identify the regions of interest for subsequent analyses. Time-frequency analyses were conducted for the inferior temporal, parahippocampal, inferior frontal, and middle occipital gyri. Phase-synchronisation was compared between conditions between 32 regions of interest. Material specific differences in neural synchrony were identified, with peak synchronisation around 1000 ms that was unique to verbal associative memory and mildly left-lateralised, compared with temporally diffuse and bilateral desynchronisation during spatial associative memory. However, overall, levels of local synchrony during verbal and spatial associative memory were more similar than different, with no compelling evidence for dissociation by material type or hemisphere. Differences in phase-synchronisation between verbal and spatial associative memory for theta and alpha oscillations suggested their role in long-range rather than local synchrony. Future research should focus on replication, further explore connectivity, and assess material-specific deficits in perceptual processing to identify deficits in memory processing.