Neurobiology of mindfulness

    Mindfulness may seem too simplistic to be of value for the treatment of trauma.  Yet, looking through the lens of neurobiology illustrates how mindfulness mitigates the negative effects of traumatic stress on the brain.

    Post-traumatic stress disorder (PTSD) is no longer viewed as an anxiety disorder.  Rather, the DSM-V includes it in a new category labeled “trauma and stress-related disorders”.  This is more in alignment with studies looking at the neurobiology of PTSD.  Hence, numerous brain imaging studies show the deleterious effects of traumatic (especially chronic) stress on the brain.  The brain is “neuroplastic”, which means that it changes itself through experience.  Unfortunately, it is this neuroplasticity that allows traumatic stress to have negative repercussions on the brain’s structure and function.

    In this first installment, we will begin with a simple overview of key brain structures involved in PTSD and we will look at the effect of mindfulness on these structures.

    The most important brain structures involved in the stress response are the amygdala, hippocampus, and prefrontal cortex. The amygdala is a collection of nuclei buried deeply in the temporal lobes.  It processes emotional input, especially fear, helplessness and horror associated with traumatic events. The amygdala also processes memories of emotionally arousing events.  The hippocampus is a specialized cortical area rolled into the medial temporal lobe.  It plays a major role in learning and memory and is involved in converting short-term memory to long-term memory.  The hippocampus exerts some restraint on the amygdala.  Finally, the prefrontal cortex is responsible for executive functions (e.g., planning, problem solving, decision making) and is hugely implicated in regulating emotions and arousal.  In fact, the prefrontal cortex is the major brain structure that can exert restraint on the amygdala.

    The brain areas mentioned above form a connected neurocircuitry that underlie adaptation to stress and fear conditioning.  There is substantial evidence that this neurocircuitry has undergone changes   in individuals with PTSD and that these changes are directly linked to the development of the symptoms. 

    In their review of neurobiology studies of PTSD, Nemeroff & Heim (2009) noted that the most reproducible finding in structural alterations of the brain is a reduced volume of the hippocampus.  Furthermore, their review of functional neuroimaging (fMRI) studies  revealed (1) hypoactivity in the hippocampus, (2) hyperactivity of the amygdala during presentation of traumatic cues and reminders and (3) hypoactivity of the medial prefrontal cortex.  Decrease thickness of the prefrontal cortex has also been associated with PTSD (Geuze et al., 2008)

    Hayes, Hayes, & Mikedis (2012) conducted a meta-analysis of brain imaging studies of individuals with PTSD and found very robust hyperactivity in the amygdala and widespread hypoactivity in the medial prefrontal cortex.  Furthermore, their analyses showed that when the medial prefrontal cortex was hypoactivated, greater amygdala activation was observed in PTSD and this correlated with symptom severity.

    Our review of studies on the neurobiology of mindfulness supports our position that the simple act of intentionally and nonjudgmentally paying attention moment by moment to our experience can exact a positive effect on PTSD symptoms.  Indeed, the practice of mindfulness correlates highly with changes in the amygdala, the hippocampus and the prefrontal cortex.  Numerous studies report a decrease in activity, or size, or grey matter density of the amygdala (Creswell, Way, Eisenberger, & Lieberman (2007); Goldin & Gross (2010); Holzel et al (2010); Lutz et al. (2013)).  Also, the hippocampus shows an increase in activity, or size, or grey matter density with mindfulness practice (Engstrolm (2010); Holtzel et al. (2011); Holtzel et al. (2008); Luders et al. (2009)).  Finally, mindfulness practice is correlated with increase in activity, or size, or grey matter density of the prefrontal cortex (Chiesa & Serretti (2010); Farb et al. (2007); Holzel et al. (2007); Holzel et al. (2013); Ivanovski & Malhi (2007); Lazar et al. (2005); Luders  et al. (2009)).

 

 

PTSD

Mindfulness

Amygdala

 activity

↓ activity
↓ volume

Hippocampus

↓ activity
↓ volume

↑  activity
↑ volume

Prefrontal Cortex

↓ activity
↓ volume

↑  activity
↑ volume

Table 1: Summary of changes in key brain structures in individuals with PTSD and in individuals who practice mindfulness.

In our next installment, we will offer a brief review of the hypothalamic-pituitary-adrenal axis (HPA axis), how it is dysregulated in individuals with PTSD, and how mindfulness may help restore a state of balance.

References

Chiesa, A. & Serretti, A. (2010).  A systematic review of neurobiological and clinical features of mindfulness meditation. Psychological Medicine, 40, 8: 1239-1252.

Creswell, J. D., Way, B. M., Eisenberger, N. I. & Lieberman, M. D.  (2007).  Neural Correlates of Dispositional Mindfulness During Affect Labeling. Psychosomatic Medicine, 69: (6), 560-565.

Engstrolm, M. (2010). Functional Magnetic Resonance Imaging of Hippocampal Activation During Silent Mantra Meditation.  The Journal of Alternative and Complementary Medicine, 16, (12): 1253-1258.

Farb, N. et al. (2007).  Attending to the present: mindfulness meditation reveals 5distinct neural modes of self-reference.  Social Cognitive Affective Neuroscience, 2, (4): 313-322.

Friedman, M. (2012).  Posttraumatic and acute stress disorders.  (5th ed.). Sudbury, MA: Jones & Bartlett Learning.

Geuze, E., Westenberg, H., Heinecke, A., de Kloel, C. S., Goebel, R., & Vermetten, E.  (2008). Thinner prefrontal cortex in veterans with post-traumatic stress disorder. Neuroimage,41, (1) 675–681.

Goldin, P. R. &  and Gross, J. J. (2010).  Effects of Mindfulness-Based Stress Reduction (MBSR) on Emotion Regulation in Social Anxiety Disorder. Emotion, 10, 1: 83–91.

Hayes, J. P., Hayes, S. M. & Mikedis, A. M. (2012).  Quantitative meta-analysis of neural activity in post-traumatic stress disorder.  Biology of Mood and Anxiety Disorders,2, 9.

Heim, C. & Nemeroff, C. B. (2009).  Neurobiology of post-traumatic stress disorder.  CNS Spectr.14 (1 Suppl 1):13-24.

Holzel. B. et al. (2013).  Neural mechanisms of symptom improvements in generalized anxiety disorder following mindfulness training.  Neuroimage: Clinical, 2: 448-458.

Holtzel B. et al. (2011). Mindfulness practice leads to increases in regional brain gray matter density.  Psychiatry Res., 191, (191): 36-43.

Holzel, B. et al (2010).  Stress reduction correlates with structural changes in the amygdala. Social Cognitive and Affective Neuroscience, 5, (1): 11-17.

Holtzel, B. et al. (2008). Investigation of mindfulness meditation practitioners with voxel-based morphometry.  Social Cognitive Affective Neuroscience, 3, (1): 55-61.

Holzel K. et al. (2007). Differential engagement of anterior cingulate and adjacent medial frontal cortex in adept meditators and non-meditators.  Neuroscience Letters, 421, 1: 16-21.

Ivanovski, B. & Malhi, G. (2007). The psychological and neurophysiological concomitants of mindfulness forms of meditation. Acta Neuropsychiatrica, 19: 76-91.

Lazar  S. et al. (2005).  Meditation experience is associated with increased cortical thickness.  Neuroreport,16, (17): 1893-1897.

Luders, E. et al. (2009). The underlying anatomical correlates of long-term meditation: Larger hippocampal and frontal volumes of gray matter.  Neuroimage, 45, (3): 672-678.

Lutz et al (2013). Mindfulness and emotion regulation—an fMRI study.  Social Cognitive and Affective Neuroscience, (online publication)