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LEAD Action News Volume 14 Number 1, October  2013, ISSN 1324-6011
Incorporating Lead Aware Times ( ISSN 1440-4966) and Lead Advisory Service News (ISSN 1440-0561)
The Journal of The LEAD (Lead Education and Abatement Design) Group Inc.
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For the Layperson: Blood Lead Levels in Early Childhood Predict Adulthood Psychopathy

Based on the article Blood Lead Levels in Early Childhood Predict Adulthood Psychopathy, by John Paul Wright, Danielle Boisvert and Jamie Vaske of the University of Cincinnati; edited for the layperson, with additions, by Anne Roberts, Editorial Team of LEAD Action News, with some definitions located by Robert Taylor, Researcher, LEAD Action News. The on-line version of the scholarly article was published in Youth Violence and Juvenile Justice July 2009 vol. 7 no. 3 208-222, and can be found at http://yvj.sagepub.com/content/7/3/208

How this article was put together

The framework of Wright et al has been followed, with headings added.

The bulk of this article consists of direct quotes from Wright et al. Quotes from Wright et al are not indicated by quotation marks. Some paragraphing has been introduced.

Statistical tables have been omitted.

Headings have been inserted.

Definitions have been inserted, and one diagram.

Where extracts from sources other than Wright et al have been used (for example, to define terms), these are in quotes.

Changes to Wright et al are mainly those of omission: e.g., citations are not included unless they form part of a sentence (e.g., “Studies by so-and-so have indicated that…), and references are not included.  English spelling has been substituted, e.g., ‘behaviour’.

Blood Lead Levels in Early Childhood Predict Adulthood Psychopathy

 Using data from the Cincinnati Lead Study, this study examines the effects of postnatal blood lead concentrations in early childhood (78 months) on adult psychopathy and six subscales [see explanation below] of the Psychopathic Personality Inventory (PPI)

What are the  Cincinnati Lead Study and the Psychopathic Personality Inventory?

The Cincinnati Lead Study (CLS) is a birth cohort recruited from late 1979 to early 1984.

A cohort is a group of people who share a common characteristic or experience within a defined period…Thus a group of people who were born on a day or in a particular period, say 1948, form a birth cohort.” (Wikipedia Cohort Study http://en.wikipedia.org/wiki/Cohort_study  Accessed July 10, 2011)

The CLS enrolled women in their first or early second trimester of pregnancy who attended four prenatal clinics within impoverished Cincinnati neighborhoods with a high concentration of older, lead-contaminated housing…376 newborns …were recruited … Of these newborns, 305 were developmentally examined at the CLS follow-up clinic when they were 3 and 6 months of age. They were followed up quarterly through age 5 yrs and semiannually from age 5 to 6.5 yrs.

A total of 250 CLS participants who were between 19 and 24 y of age and had been followed at least through the first 6 y of life participated in the current study. Thus, individuals in the current analysis had serial blood lead concentrations spanning the entire preschool and early school-age period of development…

The Psychopathic Personality Inventory (PPI) is a self-reporting inventory. The ‘subscales’ referred to above can be thought of as relating to a cluster of behaviours or attitudes. Participants rate themselves in relation to a series of statements descriptive of these behaviours or attitudes. [Ed] For example:

• I enjoy watching violent scenes in movies • In school or at work, I sometimes try to “stretch” the rules a little bit just to see how much I can get away with • I’m good at flattering important people when it’s useful to do so • When someone tells me what to do, I often feel like doing exactly just to spite them • I usually enjoy seeing someone I don’t like get into trouble • I like to (or would like to) wear expensive, “showy” clothing • I don’t take advantage of other people even when it’s clearly to my benefit* • To be perfectly honest, I usually try not to help people unless I think there’s some way that they can help me later • I sometimes lie just to see if I can get someone to believe me • I have to admit that I’m a bit of a materialist • I often tell people only the part of the truth they want to hear • I often lose my patience with people to whom I have to keep explaining things • To be honest, how much I like someone depends a lot on how useful that person is to me • I sometimes try to get others to “bend the rules” for me if I can’t change them any other way …


The results of the study [by Wright et al]  reveal that higher blood lead concentrations in early childhood are associated with higher levels of psychopathic symptoms in adulthood, controlling for the effects of gender, race, mother’s IQ, child’s intellectual achievement, and the quality of the home environment. Childhood lead levels predicted variation in [the following ‘subscales’ of the Psychopathic Personality Inventory] Machiavellian Egocentricity, Social Potency, Impulsive Nonconformity, and Blame Externalization. Overall, these results implicate lead exposure in the etiology [cause] of psychopathy.

Psychopathy and what causes it

Much debate exists on the origins of psychopathy. Some researchers argue that psychopathy is the result of environmental or social factors. For example, McCord and McCord’s (1964) literature review led them to conclude that psychopathy is a function of parental conflict, parental neglect, and erratic parental punishment. Other scholars have noted that individuals who score higher on psychopathy inventories also report that they have worse family backgrounds and more interpersonal problems than individuals who score lower on psychopathy inventories.  Marshall and Cooke’s (1999) case control study of 105 adult inmates found that psychopaths scored higher on parental antipathy, parental neglect, poor parental supervision, psychological abuse, negative school experience, negative social experience, and child antipathy to parents.

Other scholars, however, have argued forcefully that the origins of psychopathy do not lie within the social environment but within a person’s genetic and biological composition. This is expected to be true especially for individuals who score higher on inventories of callous unemotional traits. [Ed’s italics] Hare and others, for example, have asserted that psychopathy results from dysfunctions within the frontal cortex, the amygdala, and the parietal lobes in the brain. [For a description of the functions these parts of the brain, see below.]

Further discussion on what is a ‘Psychopath’ and what is a ‘Sociopath’

“The difference between a psychopath and a sociopath is somewhat blurred, at least according to the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM. The DSM-IV lists both definitions together under the heading of Antisocial Personalities because they share some common traits. Many use the terms sociopathy, psychopathy and antisocial personality disorder (APD) interchangeably. Professionals not only dispute whether there is a difference between a sociopath and a psychopath, but among those that believe there is a difference, there is dispute over what those differences are.

“Even those professionals that identify a difference note that the traits of the psychopath and sociopath are largely similar. Both psychopaths and sociopaths have a complete disregard for the feelings and rights of others. This often surfaces by age 15 and may be accompanied by cruelty to animals. These traits are distinct and repetitive, creating a pattern of misbehaviour that goes beyond normal adolescent mischief.

“Both the psychopath and sociopath fail to feel remorse or guilt. They appear to lack a conscience and are completely self-serving. They routinely disregard rules, social mores and laws, unmindful of putting themselves or others at risk.

some argue the sociopath to be less organized in his or her demeanour, nervous and easily agitated – someone likely living on the fringes of society, without solid or consistent economic support. A sociopath is more likely to spontaneously act out in inappropriate ways without thinking through the consequences.

“Conversely, some argue that the psychopath tends to be extremely organized, secretive and manipulative. The outer personality is often charismatic and charming, hiding the real person beneath. Though psychopaths do not feel for others, they can mimic behaviours that make them appear normal. Upon meeting, one would have more of a tendency to trust a psychopath than a sociopath.

 “Because of the organized personality of the psychopath, he or she might have a tendency to be better educated than the average sociopath, who probably lacks the attentive skills to excel in school. While psychopaths can fly under the radar of society, many maintaining families and steady work, a sociopath more often lacks the skills and drive for mimicking normal behaviour, making “seemingly healthy” relationships and a stable home less likely. From a criminal standpoint, a sociopath’s crimes are typically disorganized and spontaneous, while the psychopath’s crimes are well planned out. For this reason, psychopaths are harder to catch than sociopaths, as the sociopath is more apt to leave ample evidence in his or her explosions of violence. [Ed’s italics]

“Hence, while similar psychological traits might fall under the antisocial personality heading, from a social and criminalist point of view, the differences between a psychopath and a sociopath may be significant. According to experts, persons with a non-criminal history can also display lesser or varying degrees of either personality type.” (wiseGEEK accessed July 10, 2011 http://www.wisegeek.com/what-is-the-difference-between-a-psychopath-and-a-sociopath.htm)

Definitions of parts of the brain involved in psychopathy/sociopathy

Pre-frontal cortex

“The prefrontal cortex (PFC) is the very front of the brain, located right beneath the forehead. It is in the anterior (front) region of the frontal lobes. Besides being the front of the brain physically, it is responsible for the executive functions, which include mediating conflicting thoughts, making choices between right and wrong or good and bad, predicting future events, and governing social control — such as suppressing emotional or sexual urges. The prefrontal cortex is the brain centre most strongly implicated in qualities like sentience, human general intelligence, and personality.

“When the pathways between the prefrontal cortex and the rest of the brain are damaged due to head injury, massive personality changes can result. Weak interconnections between the prefrontal cortex and the rest of the brain have… been observed in criminals, sociopaths, drug addicts, and schizophrenics…

“The prefrontal cortex is fed information from all the senses, and combines this information to form useful judgments. It constantly contains active representations in working memory, as well as representations of goals and contexts. Unfortunately, the prefrontal cortex, one of the most important areas in the brain, is also one of the most susceptible to injury....” (Wisegeek http://www.wisegeek.com/what-is-the-prefrontal-cortex.htm )

The Limbic System

“The limbic system, named after the Latin word limbus for edge, is the innermost part of the brain, wrapped around the core ventricles. It is filled with cerebrospinal fluid and various clumps of white matter, which does not play much of a role in cognition.

“The limbic system is called the "old mammalian system" or the "mammalian brain" in the popular triune brain model, which splits the brain into three parts depending on their location and functions. The other parts are the reptilian brain or the brain stem, and the cerebral cortex or the neocortex. These are responsible for "lower" and "higher" behaviour respectively.

limbic system's components [include the] amygdala …

“The limbic system is the home of emotions, motivation, the regulation of memories, the interface between emotional states and memories of physical stimuli, physiological autonomic regulators, hormones, "fight or flight" responses, sexual arousal, circadian rhythms, and some decision systems. The limbic system is what gets "duped" when people get addicted to hard drugs. Because the addiction happens in the "lower," "preconscious" portion of the brain, we cannot rationally consider its effects, and therefore recovery and relapse avoidance can be difficult.” (Facebook. Accessed July 10, 2011 http://www.facebook.com/note.php?note_id=119412651407350 )


The amygdala is a core structure in the limbic system and is responsible for emotional processing, including emotional reactions and the formation of emotional memories related to specific events. Results from brain imaging studies have converged to show that the volume of the amygdala is significantly lower among individuals who score higher on psychopathy inventories compared to non-psychopathic individuals. Much research also shows that psychopaths typically lack empathy and have a hypoactive [reduced] response to negative or fear-inducing stimuli. Individuals who score high on psychopathy inventories often have trouble recognizing facial expressions of distress, often have decreased emotional and physiological sensitivity to aversive stimuli and often demonstrate less emotional responsiveness to others’ expressions of sadness or fear.

Parietal lobes

The orbital-frontal cortex and the parietal lobes are responsible for working memory, the ability to plan and organize behaviour, and behavioural inhibition. These structures also aid in the capacity to learn from experience—a hallmark deficit characteristic of psychopathy— and are deeply intertwined with the limbic system… it is now generally accepted that dysfunctions within the frontal lobe and limbic systems are related to psychopathy.

  Brain Diagram

Diagram from http://www.osovo.com/diagram/braindiagram2.htm Savio D Silva Network

The possible role of lead in brain dysfunction

If psychopathy results from brain dysfunctions, then it follows that factors which influence brain formation and development should be implicated in psychopathy. One such factor may be lead (Pb). Lead exposure has been found to be associated with deficits in frontal lobe functioning For instance, Trope, Lopez-Villegas, Cecil, and Lenkinski’s (2000) analysis of magnetic resonance spectroscopy results revealed that lead-exposed youths had a higher level of neuronal loss and damage within the frontal cortex than healthy control participants. [

The neuron (nerve cell) is the fundamental unit of the nervous system. The basic purpose of a neuron is to receive incoming information and, based upon that information, send a signal to other neurons, muscles, or glands.” (Biology Encyclopedia, accessed 10 July 2011 http://www.biologyreference.com/Mo-Nu/Neuron.html)

Meng et al.’s case control study also found that lead exposure was associated with a lower density of neurons in the frontal lobe and hippocampus (the hippocampus is part of the limbic system). Lead-exposed youths also score significantly lower on total and verbal IQ measures than healthy controls. Cecil et al.’s (2008) analysis of magnetic resonance imaging data from the Cincinnati Lead Study (CLS) revealed that childhood lead exposure corresponded to significantly lower levels of adult gray matter, especially within the frontal lobe. [Gray matter (as opposed to ‘White matter.]

“Gray matter represents information processing centers in the brain, whereas white matter represents the networking of – or connections between – these processing centers.” Intelligence In Men And Women Is A Gray And White Matter http://www.sciencedaily.com/releases/2005/01/050121100142.htm Irvine,  University of  Calif. (January 20, 2005)

Thus, results from both brain imaging studies and neuropsychological tests converge to show that lead exposure is related to deficits in brain structure and functioning, especially within the frontal lobe.

Lead exposure has also been linked to behaviours that are similar to psychopathy, such as attention deficit hyperactivity disorder and delinquency. Mendelsohn et al. (1998) found that toddlers who were exposed to lead scored significantly lower on an emotional regulation index, and they were also rated as significantly more withdrawn than healthy controls. Needleman, McFarland, Ness, Fienberg, and Tobin’s (2002) case control study of Pittsburgh youth showed that delinquents had significantly higher levels of lead in their tibia [shin bone] than non-delinquents. A prospective longitudinal study of  Cincinnati youths revealed that prenatal and postnatal blood lead levels were related to both parent-reported and child-reported delinquent behaviours.

A prospective study is a study in which the groups of individuals (cohorts) are selected on the bases of factors that are to be examined for possible effects on some outcome.

A longitudinal study is a study over time. (The Free Dictionary by Farlex)

A follow-up investigation of these youths also showed that prenatal and postnatal blood lead levels were associated with the number of criminal arrests in adulthood. These results show that a positive relationship between lead levels and antisocial behaviour has been found in studies that vary in population, age, type of measure of lead, and outcome measure. [Put most simply, a positive relationship exists between two ‘things’ (‘variables’) if, when one increases, the other increases; and when one decreases, the other decreases.]

The current study investigates whether childhood blood lead concentrations are related to psychopathy in adulthood, controlling for a range of confounders. [Confounding is an error in interpretation; for example, interpreting the carrying of matches as a cause of lung cancer, when it’s the smoking, not the carrying of matches that is the cause. (This example from ‘Defining Clinical Research 2009: Confounding and Causal inference, by Warren Browner, rds.epi-ucsf.org ) We also investigate whether childhood blood lead levels are related to the various dimensions of psychopathy, since scholars have emphasized that psychopathy is a composite of both affective and regulatory processes. Previous research has primarily focused on the relationship between lead levels and the behaviour, such as delinquent involvement and criminal conduct. Thus, it is open to empirical investigation whether lead levels are related to psychopathy overall and its affective and regulatory components.

Method used by Wright et al

The data used for this article come from the Cincinnati Lead Study [see page 1 of this article].

305 infants were assessed at 3 and 6 months. Further assessments continued at quarterly intervals through the age of 5 years. Subjects were then reassessed every six months until the child reached 6.5 years old. Three additional follow-up periods occurred at the ages of 10, 15 to 17, and most recently between 19 and 24 years. Two hundred and fifty CLS participants who had been followed from childhood to adulthood form the current study sample. There were an approximately equal number of men (49%) and women (51%) with a disproportionate number of non-White participants (90%) compared to White participants (10%). Prior analyses have found no systematic biases in sample attrition .


Blood lead level

Wright et al focussed on participants’ blood lead level at the age of 78 months for three reasons. First, prior studies show that blood lead levels in early childhood are highly volatile, reflecting environmental exposure and bioavailability. [Bioavailability is the amount of lead that is actually absorbed from exposure to given amount.]

Second, measures of blood lead in later childhood appear to stabilize and thus to reflect the accumulation of lead in the body.

Third, previous studies have used latter childhood blood lead levels, specifically at 6.5 years of age.


Adult participants completed the self-reported Psychopathic Personality Inventory (PPI) through the use of audio-assisted computer interviewing. The PPI was created to assess core psychopathic personality features originally developed by Cleckley (1941). The PPI has repeatedly been found to be a highly reliable and valid measure of psychopathy. The PPI consists of 187 questions on a 4-point Likert-type scale (0 = false, 1 = mostly false, 2 = mostly true, 3 = true). The total PPI score serves as an index of overall psychopathy. The internal consistency of the total PPI score for this sample was 0.91.

The PPI contains six subscales (see appendix of the scholarly article http://yvj.sagepub.com/content/7/3/208, which lists the questions):

(a) Machiavellian Egocentricity, which assesses the degree to which an individual uses others for their own personal gain (e.g., I could make an effective “con artist” if the situation required it);

(b) Social Potency, which assesses the degree to which the individual feels power over others (e.g., even when others are upset with me, I can usually win them over with my charm);

(c) Fearlessness, which assesses the degree to which the individual identifies himself as a risk-taker (e.g., many people think of me as a daredevil);

(d) Impulsive Nonconformity, which assesses the individual’s degree of social nonconformity (e.g., I get restless and dissatisfied if my life becomes too routine);

(e) Blame Externalization, which assesses the degree to which the individual externalizes responsibility onto others (e.g., people are frequently out to get me); and

(f) Carefree Non-Planfulness, which assesses the degree to which the individual fails to learn from past events (e.g., I often make the same errors in judgment over and over again). The internal consistencies of the PPI subscales for this sample ranged from 0.66 to 0.86.2

Five control variables were included in the analyses. The control variables included race, mother’s IQ, participant’s intellectual performance, and a measure of the HOME environment. Gender (0 = male, 1 = female) and race (0 = African American, 1 = White) were measured as dichotomous variables.

 Control variables In scientific experimentation, a control variable is the one that must not be changed throughout an experiment because it affects the dependent variables and thus affects the outcome of the experiment… Essentially, a controlled variable is what is kept the same throughout the experiment. An example of a controlled variable would be if you have experimented on plants and tested a product on two plants, the soil and the pot would be two controlled variables”.(Wikipedia)


…greater concentrations of lead in participants’ blood corresponded to significant increases in the total PPI scale…This finding implicates early blood lead levels in the development of psychopathy and provides evidence that psychopathic tendencies are linked to the toxicokinetics associated with childhood lead exposure. [Ed’s italics]

Toxicokinetics is “A subfield of toxicology that studies how toxins are absorbed by, metabolised by, and eliminated from the bodies of living things.” (Mondofacto on-line Medical dictionary www.mondofacto.com/facts/dictionary?toxicokinetics )

Childhood blood lead levels were also predictive of four of the PPI subscales. [Ed’s italics]

Children with elevated blood lead levels were more likely to score significantly higher on measures of Machiavellian Egocentricity, Social Potency, Impulsive Nonconformity, and Blame Externalization. These coefficients remained significant even after controlling for the effects of gender, race, mother’s IQ, child’s intellectual achievement, and the HOME score. Overall, these results implicate higher blood lead concentrations in psychopathic symptoms in adulthood. [Ed’s italics]


Frick and White (2008) note that psychopathy is closely connected to brain-based functions, such as reduced amygdala activation and hypoactive [underactive] metabolism in the prefrontal cortex. The connection between lead levels in childhood and adult psychopathy highlights the toxicokinetic [the passage through the body of a toxic agent] effect of lead on brain form and structure. Lead mimics calcium ions and is therefore stored in bone where it becomes bioavailable.[ Bio-availability is the presence within a living organism “of a substance in a form that allows it to be metabolized, serve as a substrate, bind a specific molecule, or participate in biochemical reactions.” (The Free Dictionary by Farlex)]

This is particularly troubling for lead-exposed pregnant women. During pregnancy, bone is mineralized and lead stores are evacuated from the mother and transported to the developing embryo. Lead passes through the blood/brain barrier where it then enters the central nervous system of the developing foetus.

[The next paragraph contains a mass of scientific vocabulary. Attempted definitions of the italicized words follow the paragraph.]

During central nervous system development, lead has the potential to damage glial cells, to activate protein kinase C, to activate the dopaminergic and serotonergic neurotransmission systems, to prevent apoptosis, to interfere with calcium binding in the hippocampus, and to influence the number of cortical neurons and their migration. Deleterious postnatal effects include damage to M-Methyl-DAspartate binding sites, which aids in learning, demylenation and axonal degeneration, neurotransmitter metabolism and activity, and postnatal neurogenesis.

Definitions of scientific vocabulary used in the preceding paragraph

Glial cells– the other brain cells (not neurons):“They surround neurons, providing them with oxygen, nutrients, and even remove dead neurons. Another thing they do is to help promote the successful transmission of neurotransmitters. There are four types of glial cells…
They are also known as the neuroglia. It should be noted that they do not conduct nerve impulses as neurons do.” (http://myroadtomedicalschool.blogspot.com/2010/09/glial-cells.html)

Protein kinase C

There is this from Wikipedia: “Protein kinase C, activated by tumour promoter phorbol ester, may phosphorylate potent activators of transcription, and thereby lead to increased expression of oncogenes, promoting cancer progression, or interfere with other phenomena.”

Glutamatergic neurotransmission

“Glutamatergic neurotransmission has been demonstrated to be involved in a variety of normal Central Nervous System functions…There are many aspects of brain development and function of excitatory amino acids that have been linked to the pathology of schizophrenia.”(‘Neurochemical Abnormalities in Schizophrenia,’ by Sutisa Nudmamud-Thanoia, Department of Anatomy, Center for Central Facility and Research Development, Faculty of Medical Science, Naresuan University,  Phitsanulok 65000, Thailand.  Naresuan University Journal 2005; 13(1): 61-72 61)

Apoptosis “is the process of programmed cell death (PCD) that may occur in multicellular organisms… Unlike necrosis, apoptosis produces cell fragments called apoptotic bodies that phagocytic cells are able to engulf and quickly remove before the contents of the cell can spill out onto surrounding cells and cause damage.

In contrast to necrosis, which is a form of traumatic cell death that results from acute cellular injury, apoptosis, in general, confers advantages during an organism's life cycle. For example, the differentiation of fingers and toes in a developing human embryo occurs because cells between the fingers apoptose; the result is that the digits are separate. Between 50 and 70 billion cells die each day due to apoptosis in the average human adult. For an average child between the ages of 8 and 14, approximately 20 billion to 30 billion cells die a day…

In addition to its importance as a biological phenomenon, defective apoptotic processes have been implicated in an extensive variety of diseases. Excessive apoptosis causes atrophy, whereas an insufficient amount results in uncontrolled cell proliferation, such as cancer.” [Ed’s italics](Wikipedia, accessed 12 July 2011)

Hippocampus Region of the brain that is associated primarily with memory. The name hippocampus is derived from the Greek hippokampus (hippos, meaning “horse,” and kampos, meaning “sea monster”), since the structure’s shape resembles that of a sea horse. The hippocampus, which is located in the inner (medial) region of the temporal lobe, forms part of the limbic system, which is particularly important in producing emotion.

The hippocampus functions in establishing long-term memory and is influenced by stress. Small changes in the blood flow or oxygenation levels of this region of the brain can serve as quantifiable markers for the emotional recognition of and response to stress. In addition, some neurons in the hippocampus are continually being formed. Therefore the hippocampus is one of only a few regions of the brain that serve as a source for neural stem cells.

Individuals who suffer damage to the hippocampus experience significant memory loss, or amnesia. This condition is marked by an inability to create new long-term memories.” (Britannica on Line eb.com)

Demylenation [Note different spelling in this reference]

“Demyelination is the loss of the myelin sheath insulating the nerves, and is the hallmark of some neurodegenerative autoimmune diseases, including multiple sclerosis, acute disseminated encephalomyelitis, transverse myelitis, chronic inflammatory demyelinating polyneuropathy, Guillain-Barré Syndrome, central pontine myelinosis, inherited demyelinating diseases such as Leukodystrophy, and Charcot Marie Tooth. Sufferers of pernicious anaemia can also suffer nerve damage if the condition is not diagnosed quickly. Sub-acute combined degeneration of the spinal cord secondary to pernicious anaemia can lead to anything from slight peripheral nerve damage to severe damage to the central nervous system affecting speech, balance and cognitive awareness. When myelin degrades, conduction of signals along the nerve can be impaired or lost and the nerve eventually withers.” (Wikipedia)

Axonal degeneration

“An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma…Axons make contact with other cells—usually other neurons but sometimes muscle or gland cells—at junctions called synapses. At a synapse, the membrane of the axon closely adjoins the membrane of the target cell, and special molecular structures serve to transmit electrical or electrochemical signals across the gap. Some synaptic junctions appear partway along an axon as it extends—these are called en passant ("in passing") synapses. Other synapses appear as terminals at the ends of axonal branches. A single axon, with all its branches taken together, can innervate multiple parts of the brain and generate thousands of synaptic terminals.” (Wikipedia)

Resumption of Wright et al

Our study, conducted on a prospective sample with ample variation in blood lead exposure, documents an association between childhood blood lead levels and adult psychopathy. Childhood blood lead levels, measured between the ages of 6 and 6.5 years, modestly predicted variation in the PPI measured 13 to 18 years later. The results remained significant despite controls for sex, race, maternal IQ, a global measure of home environment, and academic achievement.

Lead’s effect on the brain and central nervous system may be pervasive. If so, childhood blood lead levels should also predict variation in other dimensions of psychopathy, such as grandiosity, being emotionally cold, being highly manipulative, and being emotionally callous.

In 4 of the 6 subscales that compose the PPI, childhood lead levels was a significant predictor. Blood lead levels significantly predicted variation in Machiavellian Egocentrism, in Social Potency, in Impulsive Nonconformity, and in Blame Externalization.

These 4 dimensions portray an individual that is callous and unemotional, that is highly egocentric, that deflects blame for his or her behaviour onto others, and that consciously manipulates others for his own gain. These are the hallmark indicators of the classic conception of the psychopath.

The ability of childhood lead levels to predict variation in these dimensions provides additional evidence that childhood lead levels are implicated in the etiology [cause] of psychopathy. This is important for three reasons.

First, childhood lead exposure remains a pernicious problem. Even though blood lead and air lead levels have decreased substantially since 1970, the reductions have not been geographically uniform. Contemporary epidemiological estimates, for example, indicate that 25% of children in the  United States live in substandard housing where lead is prevalent in the paint, in the dust, and in the soil that surrounds the home. A majority of these children, however, are minority, usually African American, and experience elevated blood lead levels (above the 10 ug/dL [micrograms per decilitre] threshold established by the US Centers for Disease Control in 1991 – later a reference or action level of 5 ug/dL was set, in 2012) throughout their childhood. Exposure to this neurotoxicant is thus strongly correlated with social class. Participants in the CLS sample were overwhelmingly African American and scored in the two lowest categories on the Hollingshead measure of socioeconomic standing. Lead exposure may thus account, at least partially, for the connection between race and over-involvement in a range of criminal and deleterious behaviours.

Second, the linkage between lead exposure and social class highlights the interconnections between environmental sources of variance in psychopathy and biological agents that can interfere with healthy brain development. Psychopathy may have strong genetic roots but may still be affected by biological toxins that subtly, and sometimes not so subtly, damage the brain and central nervous system of the individual. In this way, the origins of psychopathy can be environmental and biological.

Genome v. Phenome

“The distinction between phenotype and genotype is fundamental to the understanding of heredity and development of organisms. The genotype of an organism is the class to which that organism belongs as determined by the description of the actual physical material made up of DNA that was passed to the organism by its parents at the organism's conception.... The phenotype of an organism is the class to which that organism belongs as determined by the description of the physical and behavioral characteristics of the organism, for example its size and shape, its metabolic activities and its pattern of movement.

It is essential to distinguish the descriptors of the organism, its genotype and phenotype, from the material objects that are being described. The genotype is the descriptor of the genome which is the set of physical DNA molecules inherited from the organism's parents. The phenotype is the descriptor of the phenome, the manifest physical properties of the organism, its physiology, morphology and behavior.” (Stanford Encyclopedia of Philosophy, as revised April 26, 2011 http://plato.stanford.edu/entries/genotype-phenotype/)

Finally, and more important, phenotypic behaviours [see above for a definition of phenotype] and beliefs that appear highly manipulative and callous and that advance the individual’s self-interest may be partially the result of damage to the central nervous system. This point may be critical to understanding the lead effect on psychopathy: Behavioural inhibition mechanisms may or may not be compromised, but the emotional subsystem of the brain may be, which is why the psychopath is egocentric and manipulative. Under this perspective, beliefs and internal working models emanate from the neural substrates of the compromised limbic system. The origin of conscious thoughts, which clearly define much of the personality of the psychopath, may be influenced by exposure to neurotoxins in general, and to lead specifically. This may help to explain why psychopaths show reduced amygdala responsivity to pain and fear stimuli and reduced amygdala activation in affective memory tasks. Lead ingestion in childhood appears to place at-risk individuals for a host of behavioural, intellectual, and emotional problems.

Our study, conducted on a prospective cohort of lead exposed individuals brings to light another important deleterious problem—that is, the characterlogical facets that form the underpinning of psychopathic thinking. Evidence has consistently shown that “criminal thinking errors” correlate strongly with criminal conduct. High-rate criminals, for instance, are significantly more likely to attribute hostile intent to others, to infer aggression from others where none may exist, and to externalize responsibility for their conduct. Explanations for these cognitive frames typically come from social learning theory.

From a learning perspective, persistent criminals have likely “learned” how to rationalize their behaviour, have learned attitudes and values conducive to offending, and have learned to constantly assess perceived threat. We offer another possibility: deficits in the limbic system of the brain, potentially caused by biological insult, produce thought patterns that are antisocial and self- and other-destructive. [Ed’s italics]Further research will have to examine this possibility, but our results and the literature on psychopathy, in general, strongly suggest this possibility.


1. We used the value from the 72-month lead measure if the 78-month lead measure had any missing values. 2. We used mean replacement for any missing values on the total PPI score and all eight

John Paul Wright, PhD, is associate professor of criminal justice in the Division of Criminal Justice at the  University of  Cincinnati. His work focuses on genetic and biological influences on human violent behaviour, life-course development of serious antisocial behaviour, and the interplay between biological processes and environmental stimuli. He has published more than 80 articles and 4 books.

Danielle Boisvert, ABD, is a doctoral candidate in the Division of Criminal Justice at the  University of  Cincinnati. Her areas of interests include biosocial criminology, life course criminology, behavioural genetics, and early intervention. Much of her research focuses on the effects of genetic and environmental factors on antisocial behaviours. She has published widely in criminology and genetics journals.

Jamie Vaske, ABD, is a doctoral candidate at the  University of  Cincinnati . Her research interests include biosocial criminology, quantitative research, and gender differences and similarities in criminal behaviour. She has published widely in criminology, genetics, and addiction journals.

Earlier Related Article:

Association of Prenatal and Childhood Blood Lead Concentrations with Criminal Arrests in Early Adulthood, by John Paul Wright, Kim N. Dietrich, M. Douglas Ris, Richard W. Hornung, Stephanie D. Wessel, Bruce P. Lanphear, Mona Ho, Mary N. Rae May 2008 issue of PLoS (Public Library of Science) Medicine http://www.plosmedicine.org/article/fetchObject.action?uri=info%3Adoi%2F10.1371%2Fjournal.pmed.0050101&representation=PDF

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