The vulnerability of working memory to distraction is rhythmic.

Recent research posits that the cognitive system samples target stimuli in a rhythmic fashion, characterized by target detection fluctuating at frequencies of ~3-8 Hz. Besides prioritized encoding of targets, a key cognitive function is the protection of working memory from distractor intrusion. Here, we test to which degree the vulnerability of working memory to distraction is rhythmic. In an Irrelevant-Speech Task, N = 23 human participants had to retain the serial order of nine numbers in working memory while being distracted by task-irrelevant speech with variable temporal onsets. The magnitude of the distractor-evoked N1 component in the event-related potential as well as behavioural recall accuracy, both measures of memory distraction, were periodically modulated by distractor onset time in approximately 2-4 cycles per second (Hz). Critically, an underlying 2.5-Hz rhythm explained variation in both measures of distraction such that stronger phasic distractor encoding mediated lower phasic memory recall accuracy. In a behavioural follow-up experiment, we tested whether these results would replicate in a task design without rhythmic presentation of target items. Participants (N = 6 with on average >2500 trials, each) retained two line-figures in memory while being distracted by acoustic noise of varying onset across trials. In agreement with the main experiment, the temporal onset of the distractor periodically modulated memory performance. These results suggest that during working memory retention, the human cognitive system implements distractor suppression in a temporally dynamic fashion, reflected in ~400-ms long cycles of high versus low distractibility.

Origin and identity of the Brokpa of Dah-Hanu, Himalayas - an NRY-HG L1a2 (M357) legacy.

Background: The Brokpas are an isolated tribal population of the Dah-Hanu villages of the Leh district of India. They speak Dardic, a sub-branch of the Indo-European language family, and are putatively identified as "pure Aryan," a hegemonic impression perpetuated by foreign tourism.Aim: To determine if the above is true by looking for an appreciable frequency of NRY-HG-R1a1(M17) signatures which are common to Indo-European language speakers of mainland India and elsewhere.Subjects and methods: We studied 75 random Brokpa males from the Dah-Hanu region, on the northern bank of the Indus river.Results: Interestingly, the Brokpa males possessed a high proportion of NRY-HG-L1a2(M357) (62.7%) that are found sporadically in India and her neighbourhood. A global analysis of this clade (present study, 214 of 3327 men from 63 populations; from the literature 56 of 873) suggested that they originated from southern India.Conclusion: The Y chromosomal studies suggest the Brokpa to be pre-Vedic settlers of the Himalayas, 9000 ybp, with an isolated evolution. The mtDNA profile shows a predominance of mtDNA HG A4 that must have arrived from outside the Indian subcontinent.