Long-term high-altitude exposure influences task-related representations in visual working memory

Abstract

Objective: Human working memory is impaired when individuals are exposed to high altitudes, however, whether the capacity of visual working memory is affected remains unclear. This study combined a lateralized change detection task and event-related potentials analysis to explore changes in visual working memory capacity among individuals who emigrated from a low-altitude environment to Tibet (a high-altitude environment).

Materials and methods: Thirty-five college students were recruited from Tibet University as the high-altitude (HA) group, and thirty-six low-altitude (LA) students were enrolled from South China Normal University (sea level) as the LA group. We measured participants' contralateral delay activity (CDA) under different memory loads.

Results: ERP component analysis showed that both the HA and LA groups reached an asymptote at memory load four. However, the contralateral and ipsilateral activity of the HA and LA groups shows different patterns. The results showed a significantly larger contralateral activity for the LA group than for the HA group at memory load one (p = 0.04, Cohen's d = 0.52) and load three (p = 0.02, Cohen's d = 0.61). Additionally, we found marginally larger contralateral activity at memory load four for the LA group (p = 0.06, Cohen's d = 0.47), but not at memory load two (p = 0.10) or load five (p = 0.12). No significant differences were observed for ipsilateral activity. In addition, we observed that the HA group performed larger ipsilateral activity than contralateral activity under each memory load, compared with the LA group.

Conclusion: These findings demonstrated that the attentional resource of long-term HA exposure is more captured by task-irrelevant information, potentially due to impaired inhibitory control, which makes it difficult for them to exclude the interference of task-irrelevant information.

Keywords: contralateral delay activity (CDA); high altitude; hypoxia; memory load; working memory.

Figure 1

(A) Trial structure of the change detection task. A change trial with a memory load of three in which the colors of the right items are to be remembered (as indicated by the arrow cue). (B) Electrode sites were used in the ERP component analysis and the calculation of contralateral, ipsilateral, and CDA waveforms when the items to be remembered were presented to the right of fixation [adapted from (27)].

Figure 2

Contralateral and ipsilateral waveforms. Collapsed across posterior electrode sites for each group at each memory load between −200 and −1,200 ms. HA, high altitude; LA, low altitude.

Figure 3

Mean K-scores (A) and accuracy (B) as a function of group and memory load. Error bars represent standard errors of the means. HA, high altitude; LA, low altitude.

Figure 4

Contralateral delay activity (CDA). HA, high altitude; LA, low altitude. (A) Mean amplitude of CDA between 300 and 450 ms after memory array onset. Error bars represent standard errors of the means. (B) Grand-average event-related potential waveforms time-locked to memory array onset show the contralateral delay activity (CDA) difference waves for each group at each memory load.

Figure 5

Topographical maps of the CDA at posterior electrode sites during the 300–450 ms time window for HA (left) and for LA (right) at five memory loads.

Figure 6

Mean amplitude of contralateral activity and mean amplitude. The epoch is 300–450 ms after memory array onset as a function of group and memory load. (A) Mean amplitude of contralateral activity. (B) Mean amplitude of ipsilateral activity. Error bars represent standard errors of the means.