Cloverleaf (ISSN 2561-6986)
The ability to focus on certain stimuli is known as sustained attention and it is one of the most fundamental units of the human perceptual system. Imagine an individual driving down a busy road in a busy city on a night with bad winter weather. Everywhere in sight there are people walking, cars honking, lights flashing and various smells. The driver sips on a coffee and at the same time is able to pay attention to the road ahead. In fact, all five of the driver’s sensory pathways are being activated. It is important to note that the sensory pathway does all of this without being overwhelmed or burning out the nervous system. The driver uses overt attention to focus on the cars directly in front of him and covert attention to look at the cars in his periphery. Not only that, but the driver is also using his divided attention to listen to the radio while still manoeuvring the car around traffic. For many drivers, all of this seems routine and not a difficult task at all. However, a common issue for many is that with age this ability to selectively attend to stimuli degenerates (Madden & Langley, 2007). On the other hand, practices like meditation have been shown to alter neuroplasticity in such a way that the ability to attend to stimuli is preserved and even improved regardless of age. This practice focuses on attending to a single stimulus for sustained periods of time and has shown to improve overall brain functionality. Meditation encourages neuroplasticity by increasing cerebral cortex thickness which leads to improved visual, auditory and tactile attention.
Focusing solely on visual attention, another common scenario can be studied through the lens of the medical field. A nurse is preparing a dose of medication “A” for her patient after she reads the label on the packaging. The nurse delivers a concentration of 0.8% while the label says to deliver a concentration of 0.08% and this results in the death of the patient. This scenario is a perfect example of inattentional blindness. The failure to read the label is not owing to negligence but rather an overload on the visual cortex. When the visual cortex is overwhelmed with stimuli, it often becomes blind to certain objects in one’s visual field. Laboratory experiments show that even brief exposures to meditation are able to reduce inattentional blindness (Schofield et al., 2015). Furthermore, other studies demonstrate that these effects on inattentional blindness go beyond the laboratory and have ecological validity. The effects extend to reduced change blindness, higher levels of concentration and even the ability to perform better on visual selective attention tasks in the presence of invalid cues (Hodgins & Adair, 2010). These effects are all visual perceptual advantages for both drivers and medical practitioners. Researchers have further concluded that the improved visual cortex function in meditators is primarily due to increased cortical thickness in the brain. Over time, due to age and other factors, the cortical thickness of the brain begins to decrease. Lazar et al. (2005) conducted a study in which the researchers demonstrated that cortical thickness in meditators is not only related to the age of the practitioner but also to their experience level. The experiment consisted of 20 participants who were advanced meditators but were not considered monks. They lived normal lives in the US with careers, families, social lives and interests other than meditation. On the other hand, the control group consisted of 15 participants with no meditation or yoga experience and accounted for differences in sex, age, race and education level. Cortical thickness was measured through a magnetization prepared rapid gradient echo imaging system. The results of the experiment showed an increase of thickness in various parts of the cerebral cortex however the the right hemisphere is the most crucial for the perceptual system. The right hemisphere reinforces the perceptual system’s vigilance, alertness and sustained attention. It is important to note that this study does not specify whether the variance in thickness was due to vascularity changes, glial volume or arborization per neuron. All three of these are possible factors as to why the results showed an increase in cortical thickness and improved function. However, this study was effective in illustrating that regular meditation results in neuroplasticity changes in the cerebral cortex, leading to improved levels of attention (Lazar et al. 2005). Likewise, a study done at McGill University revealed similar results when meditators performed better at tasks such as the Rapid Serial Visual Presentation (RSVP) task, showing that meditators are less prone to the attentional blink phenomenon to which many people fall victim. The study showed that this outcome is primarily due to thicker amounts of grey matter throughout the brain. Various MRI tests have proven that with meditation, the left superior frontal gyrus extending to the cingulate gyri have significantly higher levels of absorption due to cortical thickness. Other areas which show higher levels of absorption include the right precuneus, middle frontal gyri, the left supramarginal gyrus and the superior parietal lobule (Duncan et al, 2012). Notably, participants performed better on the Attention Network Test, the Stroop task and the Trail Making task. Furthermore, the study shows that meditation can help reduce cognitive disorders such as ADHD which is common amongst children with lower levels of cortical thickness (Duncan et al., 2012). The evidence shows that meditation not only provides a great advantage in preserving and enhancing attention in the visual perceptual system, but the effects also extend to other sensory pathways such as the auditory system.
With reference to the driving example, the perceptual system has advanced to the point where drivers can listen to the radio while still focusing their attention on the road ahead of them. There are, however, some flaws in the auditory perceptual system as it attends to stimuli. For example, many individuals have been in situations where they are talking to a friend or a colleague and midway through the conversation, they drift off into a phenomenon known as “pseudo-listening”—that is, appearing as if they are paying attention while in fact, they are completely attention-less in the conversation. This is common amongst most people, and due to certain lifestyle choices and other factors, this inability to sustain attention to auditory stimuli can deteriorate even further. A few studies have attempted to use event-related potential (ERP) brain markers and passive auditory mismatch negativity (MMN) to study the effects of meditation and auditory attention. MMN is scientifically defined as, “an auditory event-related potential that occurs when a sequence of repetitive sounds is interrupted by an occasional ‘oddball’ sound that differs in frequency or duration” (Geyer, 2008, p. 199). MMN is produced in the pre-frontal and temporal areas of the brain and is commonly used to measure functions of the auditory system. One study showed that long-term meditators have a greater sensitivity to sound both during and outside of meditation. The experiment measured three distinct ERPs related to audition: the N1, P2 and P3a. All three of these areas demonstrated greater sensitivity to sound, especially the N1 (Biedermann et al., 2016). Early automatic orientation of attention and early acoustic processing occur in the N1 and P2 (Alcaini et al., 1994; Näätänen & Picton, 1987) while attentional engagement is observed in the P3a (Polich, 2007). This experiment has focused more on the neural responses but there have been other studies which have focused more on the behavioural aspects of auditory attention. One such study used the dichotic listening task to contrast the attention levels of meditators and non-meditators. Participants were asked to listen to various sounds and detect when they heard deviation in the sound. The participants did the experiment before and after a three-month meditation retreat. Response times to the test significantly decreased after the three-month retreat (Lutz et al., 2008). Much of these results are again due to the cortical plasticity of the right hemisphere. Studies have shown reduced auditory attention in patients with right brain hemisphere damage. For example, an experiment conducted in 2005 compared three adult males who suffered right hemisphere damage due to stroke. Reduced auditory attention was consistent amongst all three patients (Hough et al., 2007). Referring to previously mentioned studies such as the ones done by Lazar et al. it can be observed that meditation positively impacts brain plasticity in the right hemisphere. No studies have been done that directly measure the effects of meditation on improved right brain hemisphere plasticity and auditory attention; however, it is likely that such a study would produce similar results to those that observed visual attention. Increased cortical thickness from meditation can be dramatically beneficial for both visual and auditory attention, and similar effects can be observed with tactile attention.
There have been numerous incidents in traffic where drivers have hit the gas instead of the brakes while driving. This is an indication of poor tactile attention while driving. On the other hand, many manual drivers know the amount of tactile attention it requires to gently lift their foot off the clutch and feel the “biting point” where the car begins to push forward. Both of these are examples of why tactile attention is important while driving. Unlike visual and auditory attentions, the brain region responsible for tactile attention is the somatosensory area of the parietal cortex (Burton et al., 1999). Before examining the importance of neuroplasticity in the somatosensory cortex, it is important to understand its function and the issues revolving around its degradation. “The primary somatosensory cortex (S1) plays a critical role in processing afferent somatosensory input and contributes to the integration of sensory and motor signals necessary for skilled movement” (Borich et al., 2015, p. 246). Lesions to the primary somatosensory cortex lead to the complete loss of tactile sense in most areas excluding the face (Taylor & Jones, 1997). To assess whether meditation alters neuroplasticity in the somatosensory cortex, both behavioural and anatomical changes seen in laboratory studies must be considered. Studies have shown that even amateur meditators can experience enhanced tactile attention from brief exposures to body-scan meditation. A University of Manchester laboratory generated an experiment where somatosensory attention was measured in 62 participants before and after a guided body-scan meditation. The results showed that the participants increased their tactile perception, sensitivity, and attention, and showed better somatosensory decision-making (Mirams et al., 2013). All of these effects could prove beneficial in both the manual driving and car braking scenarios. These benefits are not just temporary but also beneficial in the long-run neurologically due to the functional changes in the brain. Studies show that various meditation practices increase activity in the anterior cingulate cortex (Tang et al., 2010). The anterior cingulate cortex is responsible for executive processes which include the ability to pay attention and shift focus from stimulus to stimulus (Diamond, 2012), which once again proves vital in an individual’s driving abilities (visually, auditorily and tactically). As for gyrification, MRI tests in meditators show that the regions associated with the somatosensory pathway—most notably the primary somatosensory cortex—show a drastic increase in gray matter. These results are from meditators with long-term experience, hence, the gyrification properties (Luders et al., 2012). From these studies, it can be stated that meditation causes neuroplasticity changes in the brain which improve tactile attention.
Researchers studying the effects of meditation on neuroplasticity have gathered a great amount of evidence that the practice can aid in improving visual, auditory and tactile attention. The reason for this is primarily due to the benefits of meditation on increasing cortical thickness in various regions of the cerebral cortex. These results demonstrate that meditation can be used as an intervention method when dealing with clinical cases of attention deficits. Individuals with cognitive disorders such as ADHD, where many patients show a high degree of cortical thinning, can benefit from the neuroplasticity effects of meditation. Moreover, even for cortical thinning and loss of function that are the outcome of aging; meditation can be a remarkable way of preserving and enhancing auditory attention. Finally, meditation enhances tactile attention which may be beneficial for tasks such as driving. Cortical thinning and the loss of sensory attention is something which many individuals will encounter in their lifetime but practices such as meditation can take make use of neuroplasticity to reverse the symptoms.
References
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