Correlates of Theta and Gamma Activity during Visuospatial Incidental/Intentional Encoding and Retrieval Indicate Differences in Processing in Young and Elderly Healthy Participants

Abstract

Incidental visuospatial learning acquired under incidental conditions is more vulnerable to aging than in the intentional case. The theta and gamma correlates of the coding and retrieval of episodic memory change during aging. Based on the vulnerability of incidental coding to aging, different theta and gamma correlates could occur under the incidental versus intentional coding and retrieval of visuospatial information. Theta and gamma EEG was recorded from the frontotemporal regions, and incidental/intentional visuospatial learning was evaluated in young (25-60 years old) and elderly (60-85 years old) participants. The EEG recorded during encoding and retrieval was compared between incidental low-demand, incidental high-demand, and intentional conditions through an ANCOVA considering the patient's gender, IQ, and years of schooling as covariates. Older adults exhibited worse performances, especially in place-object associations. After the intentional study, older participants showed a further increase in false-positive errors. Higher power at the theta and gamma bands was observed for frontotemporal derivations in older participants for both encoding and retrieval. Under retrieval, only young participants had lower power in terms of errors compared with correct responses. In conclusion, the different patterns of power and coherence support incidental and intentional visuospatial encoding and retrieval in young and elderly individuals. The correlates of power with behavior are sensitive to age and performance.

Keywords: aging; gamma activity; incidental learning; intentional learning; theta activity; visuo-spatial learning.

Figure 1

Diagrammatic representation of the incidental/intentional visuospatial test.

Figure 2

Box plots showing the intergroup comparisons of the scores obtained by the participants in the incidental low-demand, the incidental high-demand, and the intentional visuospatial memory test. +, young vs. elderly participants, other symbols ° and * are values out of range. Mann–Whitney U test: p < 0.05.

Figure 3

Box plots showing the intragroup comparisons of the scores obtained by the participants under the incidental low-demand and the intentional visuospatial conditions. #, incidental vs. intentional scores, other symbols ° and * are values out of range. Mann–Whitney U test: p < 0.05.

Figure 4

Intergroup and intragroup comparisons of the theta band EEG absolute power values (natural logarithm) obtained during retrieval in baseline (BAS), incidental low-demand (INC-L), incidental high-demand (INC-H), and intentional (INT) conditions. Comparisons between age, conditions, and responses (correct vs. errors C, E, respectively) are shown. Values are mean ± EEM. *, difference from baseline; +, difference between young and old participants; (line), difference between correct and error responses. p < 0.01.

Figure 5

Intergroup and intragroup comparisons of the gamma band EEG absolute power values (natural logarithm) registered in retrieval, incidental low-demand (INC-L), incidental high-demand (INC-H), and intentional (INT) conditions. Comparisons between age and condition and between correct responses (C) and errors (E) are shown. Values are mean ± EEM. *, difference from baseline; +, difference between young and old participants; (line), difference between correct and error responses. p < 0.01.