Neuroscience of Human Attachment

Attachment is the ability to form human relationship bonds.  Individuals vary in their ability to develop social relationships.  The ability to form secure human relationships plays a key role in successful personal and occupational development.

Attachment theory evolved over 50 years ago.  This theory proposes all humans have an innate biological mechanism that supports social engagement.  This engagement is necessary during infancy to encourage nurturance and provision of a safe environment.

Bowlby is credited with describing attachment theory and he proposed three developmental styles of attachment.  These three attachment styles included:

• Secure attachment: an ability to easily seek and obtain support from others.  This style promotes strong bonds with parents, siblings, friends and later in life allows for bonding with a mate.
• Anxious attachment: a insecure attachment style where emotional support has often been inconsistent during childhood.  Individuals with anxious attachment develop hypersensitivity to interpersonal rejection and have anxiety in social environments.  They may develop a needy approach to relationships constantly seeking reassurance of the strength of social supports.
• Avoidant attachment: an insecure attachment style that may have been characterized by early social adverse environments.  Individuals with insecure attachment style built a wall around their life denying a need or interest in human interactions.

Emerging research in social neuroscience is providing a better understanding of brain mechanisms related to human attachment.  Vrticka and Vuilleumier of the University of Geneva in Switzerland recently published an excellent review of the neuroscience of human attachment in the journal Frontiers in Human Neuroscience.

The authors of this review begin by noting research showing attachment has profound effects in the domains of emotion processing, selective attention and memory.  Insecure attachment individuals are hypersensitive to changes in the expression of emotions in others.   Anxious attachments individuals have enhanced attention to threatening cues.  Avoidant attachment individuals inhibit the memory processing of distressful information.

The authors note social approach behavior appears regulated in specific brain regions including the ventral tegmental area, pituitary, striatum and ventral medial orbitofrontal cortex.  Social aversion appears to be regulated through the amygdala, hypothalamus, insula, anterior cingulate and anterior temporal poles.

Social behavior appears to regulated through both affective evaluation (emotional mentalization) and cognitive control systems (cognitive mentalizations).  These systems interact with hormonal and neurotransmitter domains in influencing social interactions.

The neuroscience of human attachment includes emerging research showing the importance of mental state representation of others (theory of mind).  Mothers with high sensitivity to the cries of their own infants during the post partum period show increased gray matter and fMRI BOLD responses in the prefrontal cortex, superior temporal sulcus and fusiform gyrus.  These regions have been identified as key components engaged in being aware of the emotional states of others.

The authors conclude that the neuroscience of human attachment is beginning to outline key common and distinct elements in avoidant and anxious attachment styles.  Attachment styles appear to be influenced by both environmental history as well as neurobiological factors, some of which may have strong genetic contributions.

Future neuroscience of research will need to move experiments into the "real world" and not be limited to task in brain scanners.  Additionally, future research needs to target early intervention studies in children with attachment problems to find the most effective methods to improve social outcomes.

Readers with more interest in this review are directed to the DOI link below where the free full text manuscript can be found.

Photo of great white egret from the author's files.

Vrtička, P., & Vuilleumier, P. (2012). Neuroscience of human social interactions and adult attachment style Frontiers in Human Neuroscience, 6 DOI: 10.3389/fnhum.2012.00212

Fat Gene (FTO) Linked to Alzheimer's Disease Risk

The relationship between obesity and risk for Alzheimer's disease is a controversial area of research.

Several studies have found a prospective increase in risk for Alzheimer's disease in those with obesity.  However, the association has been inconsistent.  Some studies have even found a reduced risk of later Alzheimer's disease in overweight populations.

One method to further investigate the possible obesity-Alzheimer's risk association is through direct genetic studies of genes known to be related to obesity.

Christiane Reitz and colleagues from the U.S. National Institute on Aging recently published this type of study in the journal PLOS One.

They focused on polymorphisms of the Fat and Obesity-Associated (FTO) gene.  The FTO gene is located on the q arm of human chromosome 15.  Polymorphisms associated with FTO intron 1, intron 2 and exon 2 have been linked to increased rates for obesity and also have some evidence of being linked to risk for Alzheimer's disease.

To study this issue in more detail, Reitz and colleagues conducted a single nucleotide protein (SNP) analysis of the FTO gene in Alzheimer's disease subjects and controls.  Two independent samples with a combined sample size approaching 3000 subjects were used in the SNP analysis. Additionally, they conducted a FTO gene expression analysis of Alzheimer's disease cases that had been confirmed by brain neuropathological analysis. 

The key finds from this genetic study were:

• Eight FTO SNP regions were linked to variation in risk for Alzheimer's disease
• Eleven FTO haplotypes were identified that significantly contributed to risk for Alzheimers's disease
• Gene expression studies in brain tissue of Alzheimer's disease subjects showed lower FTO gene expression compared to controls

The authors note their study findings "confirm the association between genetic variation in Intron 1, Exon 2 or Intron 2 in the FTO gene and AD".  (AD=Alzheimer's disease).

They propose several mechanisms for this association.  FTO gene status increases risk for hyperinsulinemia and type II diabetes, known risk factors for Alzheimer's disease.  They note a second potential mechanism where FTO gene status contributes to Alzheimer's disease by a vascular pathology (i.e. hypertension, lipid dysregulation, atherosclerosis).  Finally, they note obesity increases inflammatory markers by increasing adipokines and cytokines that may contribute to risk or severity of Alzheimer's disease.

This is an important study in the ongoing search to understand the effect of obesity on Alzheimer's disease risk.  Exploring genetic mechanisms is a promising approach to complement  epidemiological risk factor studies to advance our understanding of Alzheimer's disease. 

Photo of willet from the author's files. 

Reitz C, Tosto G, Mayeux R, Luchsinger JA, & the NIA-LOAD/NCRAD Family Study Group and the Alzheimer's Disease Neuroimaging Initiative (2012). Genetic Variants in the Fat and Obesity Associated (FTO) Gene and Risk of Alzheimer's Disease. PloS one, 7 (12) PMID: 23251365

Lifestyle Factors and Risk of Alzheimer's Dementia

The number of individuals suffering from Alzheimer's disease is rapidly increasing throughout the developed world.

A significant portion of this increase is explained by demographic trends as the Baby Boomer generation progresses through the high-risk age categories for Alzheimer's and other dementia.

It is important to understand potentially modifiable lifestyle risk factors that may stimulate a valid public health prevention program.

An important recent study examined lifestyle factors and risk for dementia among a cohort of Japanese American men.  

Gelber and colleagues followed a cohort of 3468 men over a period of 25 years.  The study focussed on the emergence of dementia including both Alzheimer's disease and vascular dementia.

The key components of the study design in this study included:

• Cohort characteristics: Men of Japanese ancestry born between 1900 through 1919 living in Oahu, Hawaii
• Dementia diagnosis: The cohort received regular neuropsychological screening with cognitive deficits prompting neurologist referral.  The study neurologist and two physicians made decisions about a diagnosis of Alzheimer's disease or vascular dementia using clinical information, neuropsychological testing, blood tests and brain imaging (CT or MRI) results. 
• Modifiable risk factor variables: BMI category, smoking status, physical activity level, dietary intake and alcohol consumption.  A global lifestyle low-risk group was identified that demonstrated the presence of a low risk on all four modifiable risk factors: BMI less than 22.6, never smoking, 3 or more hours per week of physical activity and high dietary score (more vegetable/fruit intake and moderate alcohol intake).

A total of 223 cases of dementia were identified during the follow up period.  The majority were assigned a diagnosis of Alzheimer's dementia (n=117), with vascular dementia a close second in frequency (n=78).  Twenty eight cases were given another cause for dementia.

High BMI, smoking and low physical activity all increased risk for overall dementia diagnosis with the following estimates for odds ratio of those with risk factor compared to those without:

• BMI: Odds ratio= 1.87
• Smoking: Odds ratio= 1.48
• Low physical activity: Odds ratio= 1.59

Diet score did not show a statistically significant association with overall dementia risk.

However, when specific type of dementia was examined, none of the individual lifestyle factors proved to be statistically associated with Alzheimer's disease risk.  BMI, smoking status and low physical activity were individually linked to increased risk for vascular dementia at odds ratios estimated at high levels than in the overall dementia group.

Men positive for all four lifestyle factors showed a 64% reduction in dementia risk, but this was primarily in reduction of risk for vascular dementia.

Finding no association between lifestyle factors and risk for Alzheimer's disease is somewhat discouraging.  It suggests that genetic factors, i.e. APOE gene status, may be resistant to the moderating effects of lifestyle changes.  

However, the study supports promotion of a healthy lifestyle approach in mid-life to reduce risk of vascular dementia.  Adopting all four factors in a healthy lifestyle promotes a significantly reduced risk of later dementia diagnosis.

Readers with a more detailed interest in the study can access the free full text article by clicking on the PMID link below.

Photo of burrowing owl from the author's files. 

Gelber RP, Petrovitch H, Masaki KH, Abbott RD, Ross GW, Launer LJ, & White LR (2012). Lifestyle and the risk of dementia in Japanese-american men. Journal of the American Geriatrics Society, 60 (1), 118-23 PMID: 22211390

Brain MRI and Enhanced Alzheimer's Drug Trials

Clinical research trials in Alzheimer's disease are hampered by insensitive outcome measures.

This effect results in the need for very expensive large sample sizes trial protocols.

Current state-of-the-art Alzheimer's trials frequently use the Minimental Status Exam (MMSE) or the cognitive subscale of the Alzheimers disease assessment scale (ADAS Cog).  These measures are imperfect and imprecise, often requiring a minimum of 200 to 300 subjects to be enrolled.

One strategy to improve Alzheimer's disease clinical trial methodology is to use more sensitive brain imaging markers to measure therapeutic response.

Ai-Ling Lin and colleagues from the University of Texas Health Science Center at San Antonio have recently reviewed the clinical research literature on this topic (citation below).  They reviewed research studies on cognitive decline using a number of brain imaging techniques including:

• High-resolution magnetic resonance imaging (MRI)
• Diffusion tensor imaging (DTI)
• Functional MRI (fMRI)
• Cerebral blood flow estimation using arterial spin labeling MRI (ASL-MRI)
• Single-photon emission computed tomography (SPECT)
• Magnetic resonance imaging spectroscopy
• Positron emission tomography (PET)

Obviously, there are many imaging tools available as potential biomarkers in Alzheimer's disease.  A key research issue is to find the most sensitive tool (or set of tools) that is valid and financially feasible.

The review covers research findings related to brain imaging markers in cognitively normal adults with genetic markers for Alzheimer's disease (APOE gene), mild cognitive impairment, the conversion of mild cognitive impairment to Alzheimer's disease and those diagnosed with Alzheimer's disease.  For the purpose of this post I will focus on their findings in those who have Alzheimer's disease.

Alzheimer's disease produces a marked increase in the volume of global and focal brain atrophy.  They note in their study the relative magnitude of yearly brain volume reduction in the 70 to 80 year age group in Alzheimer's disease compared to those without Alzheimer's disease (controls).  The data from high-resolution MRI studies show:

• Yearly global atrophy rate: 2 to 3% in Alzheimer's disease, 0.3% to 0.5% controls
• Yearly hippocampus atrophy rate: 3.0 to 5.9% in Alzheimer's disease, 1.0% to 1.7% in controls
• Yearly entorhinal cortex: 7.2% to 8.4% in Alzheimer's disease, 1.4% to 2.9% in controls

The entorhinal cortex region is a key region in assessing Alzheimer's disease related brain atrophy.  The entorhinal cortex region is highlighted in the figure on the left in blue.

Brain changes in Alzheimer's disease are also found in the default mode network assessed by MRI functional connectivity imaging and in cerebral blood flow using ASL-MRI.

The authors conclude that multimodal MRI (high-resolution MRI, functional connectivity MRI and arterial spin labeling MRI) holds promise as a powerful strategy to measure therapeutic effects in experimental drug study clinical trials for Alzheimer's disease.  They note these techniques will require validation against currently used primary outcome measures.  

However, because of the sensitivity of multimodal MRI, clinical trials may be able to reduce sample sizes to only about 20 to 25 subjects.  

This enhancement would be a big leap in Alzheimer's drug research and development.  It holds the promise of speeding up the clinical trial process and allowing for the study of more potential therapeutic compounds.

Photo of fire-tufted barbet from the San Diego Zoo is from the author's files.

Entorhinal cortex figure is a screen shot from the iPad app 3D Brain.

Lin AL, Laird AR, Fox PT, & Gao JH (2012). Multimodal MRI neuroimaging biomarkers for cognitive normal adults, amnestic mild cognitive impairment, and Alzheimer's disease. Neurology research international, 2012 PMID: 21949904

Proximity to Parent Reduces Anxious Youth Stress Response

Functional magnetic resonance imaging provides a powerful tool for understanding anxiety in children as well as adults.

This technique does not use any form of radiation and presents minimal risk for research participants.  We are beginning to better understand important mechanisms of childhood anxiety.

An innovative study of neural stress markers in children examined an important variable in childhood anxiety.  When children are studied in an fMRI scanner, they may or may not have a parent accompany them into the scanner room.  It is important to understand how parental proximity affects the anxiety tasks used in children.

Conner and colleagues from the University of Pittsburgh, Cal-Berkeley and the University of Virginia recently published a study related to this topic in the journal PLOS One. 

In their study, children with clinical anxiety underwent an anxiety task in the fMRI scanner.  Children were allowed to request that their accompanying parent stay with them in the scanner room.  If they did not request this, their parents waited in a external room during the period of the scanning. 

Children in the scanner were presented a series of words that included words with a cognitive element of physical danger, i.e. ghost, social anxiety, positive emotions and neutral words.  Children rated each word as positive, negative or neutral using a three-button glove.

The key findings from the study comparing 10 anxious children with parents in the scanning room, 10 anxious children with parents in the waiting room and 10 non-anxious control children with parents in the waiting room:

• Anxious children with parents in the waiting room showed increased brain response compared to control children to anxiety words in three areas known to be related to stress response: hypothalamus, the ventromedial prefrontal cortex and the left ventrolateral prefrontal cortex
• This stress response was attenuated in anxious children with parents in the scanning room.  Their level of response was very similar to control children.

The figure at the right highlights the medial frontal cortex.  This area was found to be important in the child stress response in the current study and is sensitive to parental proximity.

The authors of this study concluded that for anxious youth, "caregivers may act as emotion regulators".  They note that treatments that facilitate transfer of emotional regulation of anxiety from parental support to an internal self-mechanism may play a key role in advancing  anxiety disorder treatment in children.

Another important implication in this study is the potential role of parental proximity in comparing imaging studies across research centers.  Disparate results may be related to differing rates of parental proximity between research centers.

It is important to note this study did not use a randomized design as children were allowed to self-select whether they had a parent in the scanning room.  Nevertheless, this study proposes a brain mechanism related to a parental role in anxiety regulation for children who suffer from an anxiety disorder.  Interested readers can access the free full text of this manuscript by clicking on the link in the citation below.

Photo of blue curaco from San Diego Zoo from the author's files.

Image of prefrontal cortex is a screenshot from the iPad app 3D Brain.

Conner OL, Siegle GJ, McFarland AM, Silk JS, Ladouceur CD, Dahl RE, Coan JA, & Ryan ND (2012). Mom-It Helps When You're Right Here! Attenuation of Neural Stress Markers in Anxious Youths Whose Caregivers Are Present during fMRI. PloS one, 7 (12) PMID: 23236383

Early Brain Inflammation in Lupus (SLE)

I previously reviewed a brain research imaging study of patients with systemic lupus erythematosis (SLE).  This study found evidence of disruption of brain connectivity markers even before any clinical brain symptoms.

SLE is a multi-organ disease known to produce significant neuropsychiatric symptoms.  These symptoms do not affect all patients with SLE as the brain effects are highly variable in this disorder.  Studying patients with early SLE without brain-related symptoms provides insight into the timing, course and prevalence of brain pathophysiology.

A second study from the University of Texas Health Sciences Center at San Antonio, School of Medicine, Research Imaging Institute lends support to the early effect of SLE on the brain.

In this study, 85 subjects with SLE underwent brain positron emission tomography (PET).  PET imaging is a sensitive tool to assess brain glucose metabolism and brain inflammation.

The key elements of the design of this study included:

• Case identification: Newly diagnosed SLE (within 9 months of initial diagnosis) with SLE disease severity measured by the SLE Disease Activity Index (SLEDAI)
• Clinical presentation: Potential subjects with stroke were eliminated, 19 of the remaining sample had neuropsychiatric symptoms (anxiety, depression, psychosis, mononeuropathy or headache symptoms) and 17 had abnormal white matter hyperintensities or atrophy on magnetic resonance imaging (MRI).
• Imaging parameters: Fluoro-deoxy-glucose (FDG) PET imaging analysis by visual inspection and statistical analysis by SLEDIA severity scores

The key findings from the study included:

• 36 of 85 subjects (42%) showed abnormal PET images (decreased glucose uptake) on visual ratings localized to the frontal and parietal brain cortex
• Disease activity ratings correlated with white matter increases in FDG uptake in multiple brain regions including: frontal, parietal and occipital regions, subcortical temporal regions, limbic regions, cerebellar white matter and brain stem areas
• Subjects with neuropsychiatric symptoms showed hypermetabolism in frontal regions and subcortical white matter regions most notably in the corpus callosum regions
• Subjects without neuropsychiatric symptoms showed hypermetabolism that was limited to frontal lobe, anterior cingulate and corpus callosum regions

It is interesting that the study was able to identify specific brain regions (corpus callosum noted in figure to the right) of white matter inflammation in those with anxiety, depression and other neuropsychiatric symptoms.  This supports a specific regional effect of the SLE disease process on production of psychiatric symptoms commonly found in the disorder. 

The author note their study is the first study that demonstrates a "strong association between SLE disease activity and increased FDG uptake indicating inflammation of white matter of newly diagnosed SLE patients".  They argue that this finding suggest that primary brain pathology in SLE is inflammation targeting white matter vascular and microglial structures. 

This is an important study using brain imaging to better understand the mechanisms related to the neuropathology of SLE.  The study supports an early onset of brain inflammation in SLE, often before any neuropsychiatric symptoms.  

For interested readers the complete text article can be accessed by selecting the PMID link below.

Photo of eclectus parrot from the author's files. 

Ramage, A., Fox, P., Brey, R., Narayana, S., Cykowski, M., Naqibuddin, M., Sampedro, M., Holliday, S., Franklin, C., Wallace, D., Weisman, M., & Petri, M. (2011). Neuroimaging evidence of white matter inflammation in newly diagnosed systemic lupus erythematosus Arthritis & Rheumatism, 63 (10), 3048-3057 DOI: 10.1002/art.30458

What We Know About Obesity and Mortality

To begin 2013 I would like to do a series of posts related to weight, overweight and obesity on mortality and brain disorders.

This morning a new meta-analysis was published in JAMA examining the relationship between weight category and all cause mortality.  This study is receiving a significant degree of attention as it challenges a commonly held belief that even mild obesity is linked to earlier death.

The study was conducted by a research team at the Centers for Disease Control, the University of Ottawa in Canada and the National Institutes of Health.  A key focus in this analysis of all relevant published research is examining the effect of the lowest level of obesity (those with a BMI between 30 and 35).  Normal weight is considered to be in the 20 to 25 BMI range, overweight between 25 and 30.  BMI rates above 35 are considered severe obesity.

So for perspective, let's look at the cutoffs for a BMI of 25, 30 and 35 for two heights (5 foot 6 inches and 5 foot 10 inches)

• BMI 25- 155 pounds/175 pounds
• BMI 30- 185 pounds/210 pounds
• BMI 35- 215 pounds/245 pounds

So and individual who is 5 feet six inches tall would be in the overweight category from 155 to 185 pounds, mildly obese between 185 and 215 pounds and moderately to severely obese over 215.  Likewise you can substitute the relevant weight for a person 5 foot 10 inches tall by using the second weights in the above table.

I have summarized the hazard ratio estimates from the current study in the chart below.  The hazard ratio is set a 1.0 for those in the normal weight range and relevant category mortality hazard ratios are compared by BMI.  The hazard ratios are estimated from combining all relevant data of published research studies on this topic.

 The mortality hazard estimates actually are lower for the overweight and mildly obese categories in this meta-analysis.  However, only the 25-30 BMI overweight category reaches statistical significance compared to normal weight categories.  The hazard ratios suggest that for me at 5 foot 10 inches, I would need to be over 245 (BMI of 35) pounds to significantly increase my mortality risk.

This study suggests we might want to dial back a bit the public health concerns about milder amounts of obesity.  There is  no doubt that greater levels of obesity (BMI over 35) contribute significantly to earlier risk of death.  For those with lower levels of obesity, weight loss may be less important than regular aerobic exercise, eating a healthy diet and not smoking in promoting a longer life.

For those interested in calculating their own BMI, I recommend this easy web-based calculator provided by the National Heart Lung and Blood Institute.

Photo of great blue heron in flight is from the author's files.

Data from the chart comes from the original manuscript cited below.  Interested readers can access the JAMA free full manuscript by clicking here. 

Flegal KM, Kit BK, Orpana H, Graubard BI (2013). Association of All-Cause Mortality With Overweight and Obesity Using Standard Body Mass Index Categories JAMA, 309 (1), 71-82