Evaluation of emotion related potentials in alzheimer's disease

Objective: Alzheimer's Disease (AD) is a progressive neurodegenerative disease characterized by cognitive impairments. Cognitive impairments are followed by disruptions in social skills due to problems faced by patients in their recognition of facial expressions. The AH patients have shown that emotions are problematic in recognizing, understanding emotional cues and interpreting emotions and this problem causes a decrease in the quality of life of the patients with AD. In this study, it is aimed to evaluate the P100, N170 / Vertex Positive Potential (VPP) and N230 responses of AD patients to visual emotional stimuli without a cognitive load. Method: The study included 20 AD patients and 22 age-, gender-, and education-matched healthy controls. Participants were shown five different face expressions selected from the standard photo group, angry, happy, frightened, neutral and sad in five different sessions during EEG recording. P100 was the maximum positive peak in the 30-120 ms time interval; amplitude and latency values at O1, Oz and O2 electrode locations were measured. N170/VPP components were the maximum negative/positive peak in the 120-210 ms time interval and amplitude and latency values at TP7, TP8, P7, P8, O1 and O2 electrode locations for N170; Fz, FCz and Cz, electrode locations for VPP were measured. N230 was determined as the maximum negative peak in the time range of 200-360 ms and the amplitude and latency values at the F3, Fz, F4, C3, Cz, and C4 electrode locations were measured. Also, the gender difference in the groups was evaluated. Finally, correlations of emotional potentials with neuropsychological test scores were examined. Results: In the P100 amplitude analysis, the responses of individuals with AD were greater than healthy controls' except for angry facial expressions (F1,40=4.282; p=.045). In P100 latency analysis, latencies in left and mid electordes were prolonged in AD when compared to 4 healthy controls (F2,80=3.852; p=.031). N170 amplitudes were lower in AD patients for all conditions in comparison to healthy controls (F1,40=5.648; p=.022). Higher N170 amplitudes in happy face expressions compared to fearful, sad and neutral face expressions (F4,160=3.090; p=.043), and delayed N170 latencies in fearful facial expression were observed (F4,160=2.918; p=.035). In addition, AD patients showed delayed latencies in right hemisphere in happy and fearful face expressions compared to health controls (F4,160=3.538; p=.012). Across all groups higher VPP amplitudes were elicited in angry, happy and fearful face expressions than sad and neutral conditions (F4,160=4.399; p=.003). AD patients had higher VPP amplitudes in fearful and neutral face expressions in comparison to healthy controls (F4,160=5.604; p=.001). Across all groups, fearful face expression elicited the highest N230 amplitudes (F4,160=4.019; p=.011) and neutral face expressions resulted in the shortest N230 latencies (F4,160=3.189; p=.021). AD patients showed delayed latencies in happy face expression compared to healthy controls (F4,160=2.642; p=.045). Moderate to strong correlations between neuropsychological test scores and emotional potentials of the groups were observed. Conclusion: The present study showed increased latency and higher amplitudes of P100 in AD. The increase in amplitudes could be due to disrupted activation of the frontal regions and impairment in inhibitory effect of anterior regions to posterior regions. The delay in P100 latency is thought to be caused by the degeneration in the subcortical pathway that projects sensory information to the primary visual cortex. Lower N170 amplitudes were observed in AD patients compared to healthy contols. This finding draws attention to the impairment of early perceptual processing and degeneration in ventral pathway of patients. In contrast to N170 component, AD patients had higher VPP amplitudes in fearful and neutral face expressions compared to healthy controls. The reason for this difference may be the signs of patients' impairment of early perceptual processing and impaired link between the posterior facial processing areas and the prefrontal region in mild dementia which shows that the dorsal pathway is preserved relative to the ventral pathway. Delayed N230 latency in AD patients in the happy face expression suggests that the patient group has difficulty in identifying happy face expressions which could contribute to agitation in their daily life. Keywords: Alzheimer's Disease, Emotion, P100, N170, VPP, N230, Emotional Face Expression