Neuronal activity and cerebral blood flow changes in meditative states as defined in yoga texts

Abstract

Meditation is a training in awareness, which over a long period produces definite changes in perception, attention and cognition. This connection between meditation and attention has been mentioned in traditional yoga texts, particularly Patanjali’s Yoga Sutras. There are two states of meditation, focused awareness (dhäraëä) and effortless mental expansion (dhyäna). Dhäraëä is supposed to lead to meditation (dhyäna). Two non-meditative states, focused thinking (ekägratä) and random thinking (caïcalatä) have been described in the Bhagavad gétä. The practice of meditation is often associated with altered brain physiology and neuropsychological measures. Brainstem auditory evoked potentials (BAEPs) and midlatency auditory evoked potentials (MLAEPs) were studied in four mental states as described above i.e., caïcalatä, ekägratä, dhäraëä, and dhyäna. The results showed a significant increase in wave V peak latency of BAEPs during caïcalatä, ekägratä, and dhäraëä but not in dhyäna, suggesting the auditory information transmission was delayed at the inferior collicular level during caïcalatä, ekägratä, and dhäraëä (Kumar, Nagendra, Naveen, Manjunath, & Telles, 2010). MLAEPs components, the Na and Pa waves were prolonged, suggesting that auditory information at the level of the medial geniculate and primary auditory cortex (i.e., the neural generators corresponding to the Na and Pa waves) was delayed (Telles et al., 2013). Another study assessed the performance in cancellation task and attention d2 test with the digit symbol substitution test in aforementioned sessions. The performance in cancellation task was improved significantly after dhäraëä and worsened after caïcalatä (Kumar & Telles, 2009), whereas in d2 test of attention showed that after ekägratä, and dhäraëä there was an improvement in all measures of d2 test of attention and digit symbol substituion test (Raghavendra & Telles, 2012). The effect of two meditative states on long latency auditory evoked potentials (LLAEPs), P300 event related potentials with autonomic variables and cerebral blood flow changes in prefrontal cortex during cognitive task have not been studied.