Frontal midline theta connectivity is related to efficiency of WM maintenance and is affected by aging

• Published in: Neurobiology of learning and memory 2014-10, Vol.114, p.58-69
• Main Authors: Tóth, Brigitta, Kardos, Zsófia, File, Bálint, Boha, Roland, Stam, Cornelis Jan, Molnár, Márk
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Age; Aged; Aging; Aging - physiology; Brain Mapping; Cognition & reasoning; Electroencephalography; Female; Frontal Lobe - physiology; Frontal midline theta; Functional connectivity; Humans; Male; Memory; Memory, Short-Term - physiology; Middle Aged; Neuropsychological Tests; Phase lag index; Photic Stimulation; Theta Rhythm - physiology; Working memory; Young Adult
• ISSN: 1074-7427; 1095-9564
• DOI: 10.1016/j.nlm.2014.04.009

•Age related alterations of EEG functional connectivity was investigated.•EEG recorded during the delay period of a working memory task was analyzed.•The phase lag index was used to assess fronto-midline theta band connectivity.•Frontal midline theta connectivity was sensitive to memory load and later performance.•Decreased level of fronto-cortical connectivity was found in the elderly. Representations in working memory (WM) are temporary, but can be refreshed for longer periods of time through maintenance mechanisms, thereby establishing their availability for subsequent memory tests. Frontal brain regions supporting WM maintenance operations undergo anatomical and functional changes with advancing age, leading to age related decline of memory functions. The present study focused on age-related functional connectivity changes of the frontal midline (FM) cortex in the theta band (4–8Hz), related to WM maintenance. In the visual delayed-match-to-sample WM task young (18–26years, N=20) and elderly (60–71yearsN=16) adults had to memorize sample stimuli consisting of 3 or 5 items while 33 channel EEG recording was performed. The phase lag index was used to quantify connectivity strength between cortical regions. The low and high memory demanding WM maintenance periods were classified based on whether they were successfully maintained (remembered) or unsuccessfully maintained (unrecognized later). In the elderly reduced connectivity strength of FM brain region and decreased performance were observed. The connectivity strength between FM and posterior sensory cortices was shown to be sensitive to both increased memory demands and memory performance regardless of age. The coupling of frontal regions (midline and lateral) and FM-temporal cortices characterized successfully maintained trials and declined with advancing age. The findings provide evidence that a FM neural circuit of theta oscillations that serves a possible basis of active maintenance process is especially vulnerable to aging.