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Background Several researchers have reported the impairment of recognition of facial expressions in Alzheimer’s disease (AD) patients. AD had reduced theta and alpha responses compared to healthy controls during the recognition of facial expressions (Güntekin et al. 2019). Gamma responses also have a crucial role in the recognition of facial expression in healthy young adults (Güntekin and Başar 2014). AD had increased late gamma responses compared to healthy controls during working memory paradigms (Başar et al. 2017). The present study aims to analyze the gamma responses during the recognition of facial expressions in AD and healthy controls. We hypothesized that if the increase of late gamma responses is a general phenomenon in AD patients independent of the stimulation type, we expect to find increase gamma responses in AD patients in comparison to healthy controls. Method EEGs of 40 healthy controls (HCs) and 41 AD patients were recorded during their perception of three different facial expressions (angry, happy, neutral). Event‐related power spectrum and phase locking were analyzed for three different gamma bands (30‐35 Hz, 35‐ 40Hz, 40‐48 Hz) in two different time windows (0‐200 ms, 200‐400 ms). Result The group difference between AD patients and HCs was not significant for the phase‐locking values. AD patients had higher gamma power responses compared to healthy controls in 200‐400 ms time window for 30‐35 Hz(p=0.016), 35‐40 Hz(p=0.018) and 40‐48 Hz (p=0.039). The only significant group difference for the early time window (0‐200 ms) was found for 35‐40 Hz (p=0.046). The figure shows topographical plots of gamma (35‐40 Hz) power for 200‐400 ms time window in patients (upper part) and healthy controls (lower part) for angry, happy and neutral facial expressions. Conclusion The present study showed that the increase of late (200‐400 ms) gamma were independent of stimulus type in AD patients. The increase of gamma power in a 200‐400 ms time window was found in AD patients compared to healthy controls for all three facial expressions. The facial expression recognition in AD patients was differentiated from healthy controls by increased gamma power. Acknowledgments: This work (grant number 218S314) was supported by TUBITAK.

Background The performance of facial expression recognition is affected both in neurocognitive disorders and in healthy elderly. Emotional content processing is expected to be adversely affected in dementia and as well in Parkinson's disease patients. The present study aims to compare the impaired facial expression recognition between different types of dementia patients, functional connectivity changes in patients with mild cognitive impairment, and patients with dementia were investigated by event‐related EEG‐coherence. Method 25 Healthy elderly controls (HC), 25 Mild Cognitive Impairment patients (MCI), 25 patients with Alzheimer's disease (AD), 15 patients with Parkinson's disease with Mild Cognitive Impairment (PDMCI), and 16 patients with Parkinson's disease Dementia (PDD) were included in the study. EEG was recorded while angry, happy, and neutral facial expressions were presented. The artifacts were rejected by using Independent‐Component‐Analysis and Current‐Source‐Density. Magnitude‐squared coherence values of theta (4‐7Hz, 50‐400ms) responses were calculated. Inter‐hemispheric and intra‐hemispheric (frontal and central centered) pairs of F3, F4, C3, C4, T7, T8, Tp7, Tp8, P3, P4, O1, O2 channels were used. Two separate inter and intra hemispheric repeated‐measures‐ANOVA models were used for group comparisons. Result There were no group differences for intra‐hemispheric comparisons, but GroupXLocation comparison (p=.040) was significant, HE and MCI groups had higher coherence values in central‐ temporal, central‐ temporoparietal, and central‐ occipital connections compared to PDMCI, PDD, and AD patient groups (Figure 1). FaceXGroup (p=.009) interaction was significant for inter‐hemispheric coherence values, HC and MCI groups had higher interhemispheric coherence values than the PDMCI, PDD, and AD, especially during recognition of "angry" facial expression. Conclusion The connectivity between the central and posterior regions increased with emotional face content; this increase seems to be preserved in MCI. On the other hand, it wasn't maintained in patients with more severe neurocognitive impairment; PDMCI, PDD, and AD groups had reduced central‐posterior connectivity and interhemispheric connectivity during the facial expression recognition paradigm. The decrease in inter and intra‐connectivity in the posterior regions is consistent with behavioral scores and may indicate neural losses as a phenomenon.

Background Impairment of facial expression recognition in dementia is one of the cognitive deficits that could affect the social life of dementia patients. The severity of the facial expression recognition in different types of dementia has not been fully addressed. Previous studies showed that EEG event‐related oscillation (ERO) studies could reveal the brain dynamics during successful facial expression recognition. Furthermore, the impairment of facial recognition in Alzheimer's disease patients were represented with abnormal EROs (Güntekin et al., 2019). The present study aims to compare the impaired facial expression recognition between different types of dementia by analysis of event‐related delta responses. The role of delta responses in facial expression and emotional paradigms was reported previously by several researchers (Güntekin and Başar, 2014). Method 25 Healthy elderly controls (HC), 25 Mild Cognitive Impairment patients (MCI), 25 patients with Alzheimer's disease (AD), 15 patients with Parkinson's disease with Mild Cognitive Impairment (PDMCI) and 16 patients with Parkinson's disease Dementia (PDD) were included in the study. The electroencephalographic activity was recorded during the perception of the facial expression recognition task (Angry, Happy, Neutral). Delta power and phase‐locking were computed for each facial recognition stimuli and compared among the groups (ANOVA, p<0.05). Result Both delta power and delta phase locking were lower in dementia groups than healthy controls being worst in PDD. Figure 1 shows the grand average of delta power in all groups for the right occipital location. PDD (p<0.0001) and AD (p<0.05) had lower delta power than the healthy controls, the reduction of delta responses in PDD and AD were especially found over occipital locations. MCI and PDMCI subjects were found less impaired facial expression recognition compared to AD and PDMCI. Conclusion The present study showed that dementia patients had severe facial recognition deficits that increased cognitive impairment. Event‐related delta responses successfully showed the impaired recognition of facial expression in different types of dementia groups. Among all dementia subjects, PDD patients had the most reduced delta responses that could be an electrophysiological biomarker of impaired facial expression recognition. Acknowledgments: This work (grant number 218S314) was supported by TUBITAK. References: 1) https://doi.org/10.1111/psyp.13434.2) https://doi.org/10.1016/j.neuropsychologia.2014.03.014