Age-related differences in cortical activity during a visuo-spatial working memory task with facial stimuli

Abstract

Emotion, importantly displayed by facial expressions, is one of the most significant memory modulators. The interaction between memory and the different emotional valences change across lifespan, while young adults (YA) are expected to better recall negative events (Negativity Bias Hypothesis), older adults (OA) tend to focus on positive stimuli (Positivity Effect Hypothesis). This research work aims at verifying whether cortical electrical activity of these two age groups would also be differently influenced by emotional valences in a visuo-spatial working memory task. 27 YA (13 males) and 25 OA (14 males), all healthy volunteers, underwent electroencephalographic recordings (21 scalp electrodes montage), while performing the Spatial Delayed Recognition Span Task using a touch screen with different stimuli categories: neutral, positive and negative faces and geometric pictures. YA obtained higher scores than OA, and showed higher activation of theta and alpha bands in the frontal and midline regions, besides a more evident right-hemispheric asymmetry on alpha band when compared to OA. For both age groups, performance in the task was worse for positive faces than to negative and to neutral faces. Facial stimuli induced a better performance and higher alpha activation on the pre-frontal region for YA, and on the midline, occipital and left temporal regions for OA when compared to geometric figures. The superior performance of YA was expected due to the natural cognitive deficits connected to ageing, as was a better performance with facial stimuli due to the evolutionary importance of faces. These results were related to cortical activity on areas of importance for action-planning, decision making and sustained attention. Taken together, they are in accordance with the Negativity Bias but do not support the Positivity Effect. The methodology used was able to identify age-related differences in cortical activity during emotional mnemonic processing and may be interesting to future investigations.

Figure 1. Experimental design for the Spatial Delayed Recognition Span Task.

The full procedure included 40 trials of up to a maximum of 8 identical stimuli, 10 trials for each stimulus category (geometric pictures, positive, neutral and negative faces). The participant had to identify the stimulus in the new location. There was a 3-second interval of configuration (IC) between each new stimulus is presented on the touch screen.

Figure 2. Relative topographic power spectrum distribution for specific bands with each stimulus category and age group.

Stimulus categories are: geometric pictures, negative, neutral and positive faces. Age groups are: young adults (YA) and older adults (OA). Alpha activity: 8 to 13 Hz, Beta activity: 13 to 30 Hz, Gamma activity: 30 to 70 Hz, Theta activity: 4 to 8 Hz. Red dots indicate significant statistical differences (p<0.05; parametrical tests) related to age groups in electrode location.

Figure 3. Relative topographic power spectrum distribution for specific bands with type of stimulus and age group.

Types of stimulus are: geometric pictures and facial photos. Age groups are: young adults (YA) and older adults (OA). Alpha activity: 8 to 13 Hz, Beta activity: 13 to 30 Hz, Gamma activity: 30 to 70 Hz, Theta activity: 4 to 8 Hz. Red dots indicate significant statistical differences (p<0.05; parametrical tests) related to age groups and to types of stimulus in electrode location.