Recent work suggests that while voluntary episodic memory declines with age, involuntary episodic memory, which comes to mind spontaneously without intention, remains relatively intact. However, the neurophysiology underlying these differences has yet to be established. The current study used electroencephalography (EEG) to investigate voluntary and involuntary retrieval in older and younger adults. Participants first encoded sounds, half of which were paired with pictures, the other half unpaired. EEG was then recorded as they listened to the sounds, with participants in the involuntary group performing a sound localization cover task, and those in the voluntary group additionally attempting to recall the associated pictures. Participants later reported which sounds brought the paired picture to mind during the localization task. Reaction times on the localization task were slower for voluntary than involuntary retrieval and for paired than unpaired sounds, possibly reflecting increased attentional demands of voluntary retrieval and interference from reactivation of the associated pictures respectively. For the EEG analyses, young adults showed greater alpha event-related desynchronization (ERD) during voluntary than involuntary retrieval at frontal and occipital sites, while older adults showed pronounced alpha ERD regardless of intention. Additionally, older adults showed greater ERD for paired than unpaired sounds at occipital sites, likely reflecting visual reactivation of the associated pictures. Young adults did not show this alpha ERD memory effect. Taken together, these data suggest that involuntary memory is largely preserved with age, but this may be due to older adults' greater recruitment of top-down control even when demand for such control is limited.
Two-part paradigm: In the first session participants encoded a series of semantically related sound-picture pairs and a series of unpaired sounds. In the second session EEG was recorded while sounds from the encoding phase were replayed and participants had to decide whether the sound was louder on the left or right. Those in the voluntary condition were instructed to retrieve the picture associated with each sound. After the sound localization task, participants listened to the sounds again and retrospectively reported for which sounds (during the localization task) they had remembered the associated picture.
During the first session, participants were introduced to a set of semantically related sound-picture pairs, along with a series of unpaired sounds. In the second session, EEG data was recorded as participants listened to sounds from the initial phase and identified the direction of louder audio (left or right). Those in the voluntary retrieval condition attempted to recall the picture associated with each sound. Following this, participants re-heard the sounds and retrospectively noted which ones prompted picture recall during the localization task.
In accordance with Brock University principles, all age related variables are coded such that they match the mean ages of the cohorts as reported in the publication.
Participants were 31 young adults (18-30 years; M=21.06, SD=2.83; 4 males) of which 15 were in the voluntary retrieval condition. 35 are older adults (65-80 years M=71.71, SD=4.91, 10 males) of which 18 were in the voluntary retrieval condition.
We thank Tyler Kennedy Collins and Sara Stephenson for programming and technical assistance. This work was supported by the Natural Sciences and Engineering Research Council of Canada (Grant RGPIN-2017-03804 to KLC, 122222-2013 to SJS, and CGS to SEH), the Canadian Foundation for Innovation (Grant #5678 to SJS), and the Canada Research Chairs program (KLC). This research was enabled in part by support provided by Compute Ontario (www.computeontario.ca) and Compute Canada (www.computecanada.ca).
Data dissemination and standardization supported by EEGNet.Loris.ca