Objectives: Working memory (WM) deficit is present even at the early phase of Alzheimer's Disease (AD), and considered to be originated from the failure of central executive functioning. Emotional working memory (EWM) is suggested as a WM type with specific cortical representations, distinguished to processes emotional stimuli, and may or may not be spared in AD. Therefore we aimed to study WM and EWM performance and accompanying prefrontal activations in AD. Methods: Twenty AD patients were recruited from Ankara University, Faculty of Medicine, Geriatric Psychiatry Unit, along with 20 healthy elderly individuals (HE). One-back task was administered in three conditions; by employing a neutral and two emotionally charged (positive and negative) word lists as stimuli (6 target and 14 non-target words in blocks for each condition). Oxyhemoglobin (Hb02) concentrations were measured simultaneously in the prefrontal region with a 24 channel Hitachi-ETG-4000 fNIRS device. Mixed ANOVA with repeated measures was used for the analysis: 2 (group: HE and AD) x 3 (emotional valance: positive, negative or neutral).
Results: Correct response rates were similar in AD patients and HE subjects in all conditions. Reaction time was longer in AD compared to HE (F(1,37) = 4.17, p = 0.048). In HE, emotional words had no significant impact on working memory, there was no significant correlation between the reaction times, prefrontal activations and different emotional words. However, in the AD group, emotionally positive compared to neutral stimuli led to greater activations in two channels (Ch. 20 and 23) located at the right antero-lateral prefrontal area (z=-1.85, p= 0.03, z= -2.24, p= 0.01, respectively). When compared to HEs, Ch.23 activation was significantly higher in AD patients during the EWM-positive condition (U= 134 z= -1.78, p= 0.38).
Conclusion: Although, reaction time was prolonged in neutral (WM) and negative-EWM conditions, it was comparable to HE when positive stimuli were administered. Therefore, it is plausible to think that positive stimulus may have an increasing effect on EWM in AD. The activation of the right antero-lateral prefrontal area may be involved in processing emotionally positive stimuli, enhancing the WM performance in AD. The 'positivity effect' can be utilized to facilitate psychosocial and cognitive interventions in AD patients.