Switching on Behavioral and Neural Rhythmicity to Retrieve Memories When the Number of Retained Items Exceeds Four

​思い出すのが難しい記憶を人がどのようにしてなんとか思い出そうとするのかを脳波と行動計測を組み合わせて明らかにした論文。思い出すのが難しくなり、認知的な限界がくると脳波のシータ・アルファリズムを使って記憶を思い起こそうとすることを発見した。

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Abstract: Even when we experience difficulty in recalling memories, we nevertheless manage to retrieve the target items. However, the neural mechanisms that enable such difficult memory retrieval are unknown. Here, we report an intriguing phenomenon where our nervous system “switches on” behavioral/neural rhythmicity to retrieve memory when the number of candidate items exceeds four. In our experiments, participants learned and retrieved 2–5 color/letter pairs. Analyses of hundreds of reaction times revealed a significant tendency for memory recall to occur at discrete times corresponding to theta–alpha (4–13 Hz) cycles, but only when the number of memorized pairs exceeded four. Electrophysiological data localized theta–alpha rhythmicity around parietal electrodes, a region associated with the long-term memory system. Our findings suggest that neural rhythmicity facilitates memory retrieval when the number of candidate items exceeds four, which is known as the “magical number” corresponding to the limit of human cognitive capacity.

The flow state is not accompanied by frontal-midline theta activity: An EEG investigation of more than 700 video gameplay sessions

実際のゲームプレイ中の脳波を 1被験者あたり10日間にわたって、100試合以上計測した研究。フロー・ゾーン状態の神経基盤を明らかにすることを目的としておこなった。フロー状態は前頭葉の強力なトップダウン制御であるという従来の仮説を否定した。

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Abstract: People sometimes experience a “flow state”—characterized by hyperfocus, time distortion, and loss of self-awareness—during sports or video gameplay. Previous neuropsychological studies using simple laboratory tasks have reported that the flow state is associated with activation in the frontal lobe, reflected in theta (4–7 Hz) band rhythmic neural activity in medial prefrontal regions (frontal-midline theta [FMT] activity). However, the findings of previous studies might be problematic because they did not appropriately capture the neural activity associated with the flow state for the following reasons: 1) they used unfamiliar and unmotivating tasks; 2) they defined the neural basis of the flow state as neural activity occurring during tasks of optimal difficulty, disregarding trial-to-trial variations in subjective experience of the flow state; 3) the duration of the experiment or the number of trials was not sufficient to capture the rare experience of flow; or 4) they ignored individual differences in neural activities related to flow experiences. Thus, we examined the relationship between the flow state and FMT activity, recorded via scalp electroencephalography, in an experimental paradigm that addressed these four issues. First, participants played their favorite competitive video games, which they had been routinely playing. Second, task difficulty was kept as uniform as possible across trials by employing rank matching to directly examine the correlation between subjective flow level and FMT activity across trials. Third, to address the concern regarding the low frequency of the flow experience, more than 100 trials were completed over 10 days by each participant. Lastly, we adopted a within-participant statistical approach to examine individual differences in the nature of the flow experience. The results showed no correlation between FMT activity and the degree of subjective flow in six out of seven participants, contrary to previous reports. Our results challenge the conventional view that frontal lobe activity, as reflected in FMT activity, is instrumental in entering into the flow state.

Behavioral fluctuation reflecting theta-rhythmic activation of sequential working memory

人の認知処理に不可欠であるとされるワーキングメモリの神経表現を行動学的データから明らかにした研究。

ワーキングメモリ課題時の行動データに律動がみられることから、位相依存的な神経表現が脳内にあることを大規模な計測を用いて明らかにした。

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Abstract: Sequential working memory, the ability to actively maintain sequential information, is essential for human cognition. The neural representation of each item in sequential working memory is thought to be activated rhythmically within the theta (3–7 Hz) range of human electrophysiology. In the current study, we predicted that if neural representations of sequential working memory items were truly activated rhythmically, periodic fluctuations in behavior would be evident. That is, the ease and speed of recalling each memory item would oscillate depending on the interval between memory encoding and recall, affected by the rhythmic neural representation. We conducted detailed analyses of reaction times for retrieving sequential and non-sequential information in eight experiments (total n = 125). The results revealed that reaction times for recalling sequential information showed fluctuation in the theta range as a function of the interval between memory encoding and recall, which was significantly stronger than that observed when the task did not require participants to remember the sequential order. Taken together, the current findings revealed that participants’ behavior exhibited theta-rhythmic fluctuation when recalling sequential information in a relatively large sample, supporting theta phase-dependent coding of sequential working memory.

Gymnasts' Ability to Modulate Sensorimotor Rhythms During Kinesthetic Motor Imagery of Sports Non-specific Movements Superior to Non-gymnasts

アスリートが持つ鮮明な運動イメージ能力を脳波を用いて検証した研究。アスリート（体操選手）は実際の運動時と同様の脳活動状態に、イメージのみで脳活動を変調することができることを示した。

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Abstract: Previous psychological studies using questionnaires have consistently reported that athletes have superior motor imagery ability, both for sports-specific and for sports-non-specific movements. However, regarding motor imagery of sports-non-specific movements, no physiological studies have demonstrated differences in neural activity between athletes and non-athletes. The purpose of this study was to examine the differences in sensorimotor rhythms during kinesthetic motor imagery (KMI) of sports-non-specific movements between gymnasts and non-gymnasts. We selected gymnasts as an example population because they are likely to have particularly superior motor imagery ability due to frequent usage of motor imagery, including KMI as part of daily practice. Healthy young participants (16 gymnasts and 16 non-gymnasts) performed repeated motor execution and KMI of sports-non-specific movements (wrist dorsiflexion and shoulder abduction of the dominant hand). Scalp electroencephalogram (EEG) was recorded over the contralateral sensorimotor cortex. During motor execution and KMI, sensorimotor EEG power is known to decrease in the α- (8–15 Hz) and β-bands (16–35 Hz), referred to as event-related desynchronization (ERD). We calculated the maximal peak of ERD both in the α- (αERDmax) and β-bands (βERDmax) as a measure of changes in corticospinal excitability. αERDmax was significantly greater in gymnasts, who subjectively evaluated their KMI as being more vivid in the psychological questionnaire. On the other hand, βERDmax was greater in gymnasts only for shoulder abduction KMI. These findings suggest gymnasts' signature of flexibly modulating sensorimotor rhythms with no movements, which may be the basis of their superior ability of KMI for sports-non-specific movements.