شکل پذیری قشر، تنوع منفی احتمالی، و تجارب متعالی در طول تمرین روش متعالی مدیتیشن
|کد مقاله||سال انتشار||تعداد صفحات مقاله انگلیسی||ترجمه فارسی|
|31791||2000||5 صفحه PDF||سفارش دهید|
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Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Biological Psychology, Volume 55, Issue 1, November 2000, Pages 41–55
This study investigated effects of transcendent experiences on contingent negative variation (CNV) amplitude, CNV rebound, and distraction effects. Three groups of age-matched subjects with few (<1 per year), more frequent (10–20 per year), or daily self-reported transcendent experiences received 31 simple RT trials (flash (S1)/tone (S2)/button press) followed by 31 divided-attention trials — randomly intermixed trials with or without a three-letter memory task in the S1–S2 interval). Late CNV amplitudes in the simple trials were smallest in the group with fewest, and largest in the group with most frequent transcendent experiences. Conversely, CNV distraction effects were largest in the group with fewest and smallest in the group with most frequent transcendent experiences (the second group's values were in the middle in each case). These data suggest culminative effects of transcendent experiences on cortical preparatory response (heightened late CNV amplitude in simple trials) and executive functioning (diminished distraction effects in letter trials).
Experience-related cortical plasticity was first identified during critical periods of development. Sensory experiences establish the appropriate orientation and interconnection of cortical receptor fields (Hubel and Weisel, 1977) and is required for mature functioning of pattern recognition abilities (von Senden, 1960). Recent research suggests that experience shapes cortical connectivity not just during critical periods in development but throughout the life span. Even in adult human and primates, sensory, motor and sub-cortical representations are continually shaped by experience (Gilbert, 1993, Donoghue, 1995, Wang et al., 1995 and Buonomano and Merzenich, 1998). For instance, string players have distinctly larger cortical representations in the primary somatosensory cortex of the fingers of their left hand (the hand that forms the chords) than do non-musicians (Elbert et al., 1995). Elbert et al. (1997) suggest that consciously performing any task regularly over time may lead to cortical reorganization. This generalization is based on research that has primarily focused on the effect of overt behavior on reorganization of sensory and motor cotius. The cortical maps for these areas are well defined. Consequently, any structural changes are (fairly) straightforward to locate and to quantify. The quality of experience also seems to shape cortical structure. Repeated stressful experiences lead to high secretion of glucocorticoids, which are thought to lead to decreased hippocampal mass (Sapolsky, 1996). Decreased hippocampal mass is reported in depressed patients and individuals diagnosed with post-traumatic stress disorder. Stress also plays an important role in decreasing cortical blood flow and adversely affecting behavior (Amen and Carmichael, 1997). Our research has focused on the effects of transcendent experiences during Transcendental Meditation® (TM®) practice1 on brain functioning. Transcendent experiences during TM practice are phenomenologically and physiologically distinct from other waking eyes-closed experiences and occur many times in each TM session. These experiences are subjectively characterized by ‘silence’ and the ‘loss of boundaries of time, space and body sense’ (Travis and Pearson, 2000; see also Maharishi, 1963). Time, space and body sense are the framework that give meaning to waking experiences (Velmans, 1993). During transcendent experiences, the very framework of ordinary waking experience is absent. In addition, these transcendent experiences are physiologically distinct from other eyes-closed states. Transcendent experiences are characterized by apneustic breathing up to a period of 40 s, with autonomic orienting at their onset (Travis and Wallace, 1997). Apneustic breathing has not been reported in non-clinical populations and, even in clinical populations, never for longer than 4–6 s (Plum and Posner, 1980). In addition, high amplitude global alpha activity is reported during transcendent experiences suggesting stable thalamo-cortical oscillations during this state (Travis and Wallace, 1999). Based on these unique phenomenological and physiological markers, Travis and Pearson (2000) argued that transcendent experiences during TM practice might constitute a unique state of consciousness (traditionally) called ‘Transcendental Consciousness’ (Maharishi, 1963) rather than an altered state of waking. While there is no evidence for structural changes through regular transcendent experiences during TM practice, evidence is growing for experience-related functional changes in a number of physiological systems. A quantitative meta-analysis ( Dillbeck and Orme-Johnson, 1987) reported that meditating subjects exhibited lower basal arousal as suggested by significantly lower breath rates, heart rates, skin conductance levels and plasma lactate levels compared with controls. A comparison of age-matched subjects revealed significantly higher alpha power and coherence during eyes-open periods in subjects reporting more frequent transcendent experiences ( Travis, 1991). Contingent negative variation (CNV), a measure of cortical preparatory processes, is enhanced immediately after a TM session ( Paty et al., 1977) as well as being higher in subjects reporting more frequent transcendent experiences ( Travis, 1998). Regular transcendent experiences are also reported to lead to enhanced nervous system functioning as measured by faster paired H-reflex, a measure of neural transmission speed ( Dillbeck et al., 1981), inspection time, a measure of speed of perceptual processing ( So Kam Tim, 1995), and choice reaction time, a measure of decision time and performance speed ( Cranson et al., 1991). The TM technique is practiced with eyes closed for 15–20 min in the morning and evening. It does not involve procedures practiced during eyes-open tasks. Thus, changes in performance outside of the TM session, i.e. during task performance, most probably reflect long-term effects of transcendent experiences occurring during the 15–20 min TM sessions in the morning and evening. In the current study, we further probed possible effects of transcendent experiences on brain functioning as reflected in the CNV. The CNV is a slow increase in scalp recorded negativity observed in the interval between a warning or preparatory stimulus (S1) and an imperative stimulus (S2) that requires a response (Walters et al., 1964). When probe stimuli (like a short-term memory task) are introduced in the S1–S2 interval the amplitude of the late CNV decreases and reaction times slow, which is called a CNV distraction effect. When distracting stimuli are randomly omitted, late CNV amplitudes increase beyond baseline values, called CNV rebound, but reaction times again slow relative to baseline trials (Tecce, 1979 and Travis and Tecce, 1998). CNV amplitudes reflect processing resources (Kok, 1997), and the interaction between attention to task and arousal levels (Tecce et al., 1976). Transcendent experiences, which are described in terms of heightened inner alertness, may activate processing resources leading to greater attention to task. If transcendent experiences systematically affect processing resources, then CNV amplitude, CNV rebound and CNV distraction might be expected to fall on a ‘dose–response’ curve — systematically increasing with increasing frequency of transcendent experiences.