Williams Syndrome Research Paper
Running Head: AMYGDALA & HYPERSOCIABILITY
The Role of the Amygdala and Abnormal Social Behavior in Williams Syndrome
Abstract
Williams syndrome (WS) is a genetic neurodevelopmental disorder often paired with unique behavioral abnormalities like hypersociability, reduced fear and a tendency to approach strangers. The amygdala is an integral component of the neural network and has been implicated in social phenotype particularly in emotion and fear. Functional magnetic resonance imaging (fMRI) and blood-oxygenation-level-dependent (BOLD) responses indicated abnormal structure and function of amygdala in individuals with WS during face processing tasks. In healthy individuals amygdala activity is controlled by dense axonal projections of the prefrontal …show more content…
cortex. Abnormal social fearlessness may result from a failure of the orbitofrontal cortex (OFC) to inhibit amygdala responses during non-social fear processing. Together, these neurologic mechanisms may underline the abnormal function of the amygdala and contribute to profile specific responses and behavioral phenotypes observed in WS individuals.
“Williams syndrome (WS) is a rare genetic neurodevelopmental disorder caused by a hemizygous microdeletion of about 25 genes on chromosome 7q11.23 with a prevalence of 1 in 7500 births” (Avery et al., 2011). One of the most apparent behavioral traits is hypersociability which is characterized by contrasted non-social fear, overfriendliness and tendency to approach strangers. Social interaction is an integral part of every individuum. Recent studies have focused on brain areas associated with social functioning in order to propose and implement techniques that will help individuals with WS to acquire normal societal development. Research studies are expected to find possible causes for atypical amygdala structure and function and provide possible mechanisms that result in distinctive social behaviors. (Haas, B.W., Reiss, A. 2012).
First described and discovered by J.P.C. Williams and his colleges in 1961 characterized by distinct phenotype, “elfin facial features, mental developmental delay, hypercalcemia and supravalvular aortic stenosis” (Williams JCP, Barratt-Boyes BG, Lowe JB., 1961). Perhaps the most prominent behavioral phenotype is hypersociability described by over-friendliness, a strong desire for social engagement, lack of stranger fear and anxiety (Haas, B.W., Reiss, A. (2012). Early development in WS is marked by low birth weight, gastroesophageal reflux, and ineffective breast feeding (Tsai et al., 2008). Most children exhibit low IQ levels, atypical verbal development, suffer from cardiovascular abnormalities and show facial dysmorphies which may not be evident until 1.5-2 years of age. Motor development delay is observed in both children and adults (Tsai et al., 2008). Notable interest in face processing and increased sociability is observed early in life. Studies have found that infants (8-43 months) with WS showed greater gaze duration at their mothers than the control group did. Moreover, individuals with WS spent the same time looking at a stranger, suggesting high sociability and enhanced affiliative drive (Mervis et al., 2003). Children with WS (ages 8-13) commented more frequently on peripheral features such as earrings or other physical traits than did controls which tend to comment on typical features such as eyes and mouth. Interestingly, it has been noted that in individuals with WS concentration on peripheral features declines with age (Martens et al., 2009).
Williams syndrome is coupled with abnormal functions of brain regions underlying mechanisms involved in emotion and face processing. One of the mostly hypothesized brain region involved in neural network is the amygdala. Amygdala is an almond-shaped nuclei located deep inside of the medial temporal lobe (Stefanacci, L., Amaral, D.G., 2002) and plays a crucial role in emotion recognition and facial expressions (Capitao et al., 2011a), fear (Haas et al. 2010a), approachability (Martens et al., 2009), social/ non-social related stimuli (Thornton-Wells et al., (2011) and hypersociability (Capitao et al.2011b). Magnetic resonance imaging (MRI) studies have demonstrated a relative increase in total intracranial amygdala volume in individuals with WS (Capitao et al., 2011b). In addition, the mean right and left amygdala volumes were reported to be larger in WS compared to controls (Martens et al., 2009). Moreover, Martens et al., (2009) reported a relationship between the right amygdala volume and approachability ratings when pictures of “positive” faces were shown to the individuals with WS. This evidence is consistent with the results obtained by Haas et al., (2009b) and Meyer-Lindenberg, et.al., (2005). However, in the study by Haas et al., (2009b) no significant amygdala activation to negative stimuli was observed in WS individuals as compared to the control group who demonstrated an increased activity in the right amygdala to fearful social stimuli.Conversely, Martens et al.(2009) noted predominantly positive correlation between increased amygdala volume and “negative” faces in individuals with WS, which is incongruent with the results obtained by Haas et al., (2009b). Furthermore, Thornton-Wells et al., (2011) asserted that when viewing neutral face stimuli, individuals with WS had an increased amygdala response and were more likely to perceive neutral faces as happy expressions, implying social positivity attitude in WS. These studies suggest that individuals with WS have an atypical amygdala structure and function which underline possible explanations of increased sociability in people with WS.
Individuals with WS tend to show high approachability and low social inhibition levels. A feasible explication of extreme sociability behavior can be related to non-social fear or lack of it. For example, Thornton-Wells et al., (2011) reported higher left amygdala blood oxygen level dependent (BOLD) responses in individuals with WS when viewing fear non-social stimuli. Conversely, when viewing fear social stimuli, WS individuals did not show smaller amygdala BOLD responses as expected in fact, they showed an increased BOLD response to fear social images. This contradicts with the results obtained from Haas et al.,(2009b), who observed attenuated BOLD amygdala responses to fear faces. The inconsistency of these results might be due to the experimental design differences. In Thornton-Wells et al., (2011) experiment a block design with passive viewing was used, whereas in Haas et al., (2009b) event-related design which required a motor response was used.
Amygdala response is crucial for avoidance behavior (Meyer-Lindenberg et al., 2005) therefore, abnormal activation of amygdala to fear faces may contribute to social disinhibition and reduced fear of strangers. WS individuals had trouble recognizing sad and scared emotions (Capitao et al.,2011a). Interestingly, WS individuals identified angry facial emotions the same as their matched mental and chronological controls, implying that they were able to associate angry faces with a potential social threat (Capitao et al., 2011a). This finding gave raise to a hypothesis that people with WS are actually able to distinguish between approachable and non approachable people, but they cannot integrate this information and act accordingly to their social knowledge. In another study, Haas et al., (2009a) described social fearlessness and demonstrated that individuals with WS had an increased tendency to approach strangers. Less left amygdala response to fear stimuli was observed thus, suggesting a model for social fearlessness in WS. Accordingly, lateralization of amygdala function was ascribed to the left. Conflicting with the study done by Martens et al., (2009) between amygdala structure and approachability, lateralization of amygdala structure was attributed to the right. The inconsistency of the results suggests that lateralization of amygdala may account for both structure and function. Abnormalities in the amygdala relate to a failure in recognizing potential threat in the environment and therefore, acquiring trustworthiness and approachability of unfamiliar strangers (Martens et al. 2009). Together, these findings highlight that abnormal social behavior and decreased fear to approach strangers may be proportional to the amygdala structure and function. Atypical function of the amygdala may result from a disrupted orbitofrontal cortex (OFC) which is activated differently and is functionally disconnected from the amygdala in individuals with WS (Meyer-Lindenberg et al. 2005). It has been noted that both medial prefrontal cortex (MPFC) and OFC are interrelated with both the amygdala and dorsolateral prefrontal cortex (DLPFC) and play a crucial role in regulation of amygdala (Meyer-Lindenberg et al. 2005). Meyer-Lindenberg and colleagues (2005) showed that individuals with WS failed to activate OFC region in response to fear faces, whereas both MPFC and DLPFC were equally responsive during face tasks. Additionally, path analyses demonstrated a functional disconnect between OFC with either amygdala or DLPFC and found that OFC did not participate in regulatory interactions with amygdala in individuals with WS in response to threatening faces. Controls on the other hand showed a strong connection between the OFC and amygdala. Together these findings may propose that disruption in amygdala-prefrontal circuitry in individuals with WS may potentially be the evidence for atypical social processing. Bidirectional pathways linking the amygdala and orbitofrontal cortex may underline the experience of emotions (Ghashghaei, H.T., Barbas, H., 2002). Axons from the OFC project densely onto the amygdala (Stefanacci, L., Amaral, D.G., 2002) and synapse inside GABAergic nuclei underlying that OFC areas execute control on the internal processing of the amygdala (Ghashghaei, H.T., Barbas, H., 2002). In the recent study by Avery S.N, Thornton-Wells T.A (2011) scientists suggested that unsuccessful inhibition of the amygdala by OFC may attribute to amygdala hyperactivity. Likewise, they implied that structural abnormality of myelinated axons may be a plausible mechanism leading to anomalies in prefrontal-amygdala inhibitory pathways in WS individuals. The results showed reduced white matter integrity in the prefrontal and amygdala regions in individuals with WS compared to controls. This finding could possibly explain .the OFC-amygdala functional disconnect previously described by (Meyer-Lindenberg et al., 2005). In addition, white matter integrity deficits may underline a neural mechanism for the excessive amygdala hyperactivity and elevated non-social fear in WS individuals (Avery S.N, Thornton-.Wells T.A 2011). However, very little research has been done regarding this matter and due to limitations such as small sample size these results should be interpreted with vigilance. Causes of amygdala hyperfunction are in part genetic, resulting from a deletion of certain genes. Individuals with WS exhibited variations in fMRI and BOLD responses and increased tendency to approach strangers indicating abnormalities in amygdala structure and function. Neural mechanisms underlining atypical processes are associated with white matter integrity deficit and a failure of OFC to inhibit amygdala responses during non-social fear behavioral tasks. Together these findings contribute to hypersocial behavior model in WS individuals. However, studies produce contradicting evidence and further research needs to be conducted to link amygdala structure, function, the role of OFC and white matter integrity deficits.
References
Avery, S.N., Thorton-Wells, T.A., Anderson, A.W., Urbano Blackford, J (2011).White matter integrity deficits in prefrontal–amygdala pathways in Williams syndrome, NeuroImage 59 887-894
Capitao, L., Sampaio, A., Sampaio, C., Fernandez, M., Sousa, N., Pinheiro, A., Goncalves, O.F (2011a)Williams syndrome hypersociability: A neuropsychological study of the amygdala and prefrontal cortex hypothesis.
Research in Developmental Disabilities. 32, 1169-1179
Capitao, L., Sampaio, A., Sampaio, C., Vasconcelos, C., Fernandez, M., Garayzabal, E., Shenton, M. E., and Goncalves, O. F. (2011b) MRI amygdala volume in Williams Syndrome. Research in Developmental Disabilities. 32, 2767–2772
Ghashghaei, H.T., Barbas, H., (2002). Pathways for emotion: interactions of prefrontal and anterior temporal pathways in the amygdala of the rhesus monkey. Neuroscience
115, 1261–1279.
Haas, B. W., Hoeft, F., Searcy, Y. M., Mills, D., Bellugi, U., and Reiss, A. (2009a). Individual differences in social behavior predict amygdala response to fearful facial expressions in Williams syndrome. Neuropsychologia 48, 1283–1288.
Haas, B. W., Mills, D., Yam, A., Hoeft, F., Bellugi, U., and Reiss, A. (2009b). Genetic Influences on Sociability: Heightened Amygdala Reactivity and Event-Related Response to Positive Social Stimuli in Williams Syndrome The Journal of Neuroscience 29(4),
1132-1139.
Haas, B.W., Reiss, A. (2012). Social brain development in Williams syndrome: the current status and directions for future research, Frontiers in Psychology 3 (186), 1-13
Martens, M. A., Wilson, S. J., Dudgeon, P., and Reutens, D. C. (2009).
Approachability and the amygdala: insights from Williams syndrome. Neuropsychologia 47, 2446–2453.
Mervis, C. B., Morris, C. A., KleinTasman, B. P., Bertrand, J., Kwitny, S., Appelbaum, L. G., and Rice, C. E. (2003). Attentional characteristics of infants and toddlers with Williams syndrome during triadic interactions. Dev. Neuropsychol. 23,
243–268
Meyer-Lindenberg, A., Hariri, A.R., Munoz, K.E., Mervis, C.B., Mattay, V.S., Morris, C.A.,
Berman, K.F., (2005). Neural correlates of genetically abnormal social cognition in
Williams syndrome. Nature Neuroscience 8, 991–993.
Meyer-Lindenberg, A, Mervis, CB, Berman, KF., (2006). Neural mechanisms in Williams syndrome: a unique window to genetic influences on cognition and behaviour. Nature Neuroscience 7, 380–393
Stefanacci, L., Amaral, D.G., (2002). Some observations on cortical inputs to the macaque monkey amygdala: an anterograde tracing study. J. Comp. Neurol. 451, 301–323.
Thorton-Wells T.A., Avery S.N., Urbano-Blackford J. (2011). Using novel control groups to dissect the amygdala’s role in Williams syndrome. Developmental Cognitive Neuroscience 1, 295-304
Tsai, S.W., Wu, S.K., Liou, Y.M., Shu, S.G., (2008). Early development in Williams Syndrome. Pediatrics International 50, 221–224
Williams’s JCP, Barratt-Boyes BG, Lowe JB (1961). Supravalvular aortic stenosis. Circulation
24, 1311–1318.
The Role of the Amygdala and Abnormal Social Behavior in Williams Syndrome
Abstract
Williams syndrome (WS) is a genetic neurodevelopmental disorder often paired with unique behavioral abnormalities like hypersociability, reduced fear and a tendency to approach strangers. The amygdala is an integral component of the neural network and has been implicated in social phenotype particularly in emotion and fear. Functional magnetic resonance imaging (fMRI) and blood-oxygenation-level-dependent (BOLD) responses indicated abnormal structure and function of amygdala in individuals with WS during face processing tasks. In healthy individuals amygdala activity is controlled by dense axonal projections of the prefrontal …show more content…
cortex. Abnormal social fearlessness may result from a failure of the orbitofrontal cortex (OFC) to inhibit amygdala responses during non-social fear processing. Together, these neurologic mechanisms may underline the abnormal function of the amygdala and contribute to profile specific responses and behavioral phenotypes observed in WS individuals.
“Williams syndrome (WS) is a rare genetic neurodevelopmental disorder caused by a hemizygous microdeletion of about 25 genes on chromosome 7q11.23 with a prevalence of 1 in 7500 births” (Avery et al., 2011). One of the most apparent behavioral traits is hypersociability which is characterized by contrasted non-social fear, overfriendliness and tendency to approach strangers. Social interaction is an integral part of every individuum. Recent studies have focused on brain areas associated with social functioning in order to propose and implement techniques that will help individuals with WS to acquire normal societal development. Research studies are expected to find possible causes for atypical amygdala structure and function and provide possible mechanisms that result in distinctive social behaviors. (Haas, B.W., Reiss, A. 2012).
First described and discovered by J.P.C. Williams and his colleges in 1961 characterized by distinct phenotype, “elfin facial features, mental developmental delay, hypercalcemia and supravalvular aortic stenosis” (Williams JCP, Barratt-Boyes BG, Lowe JB., 1961). Perhaps the most prominent behavioral phenotype is hypersociability described by over-friendliness, a strong desire for social engagement, lack of stranger fear and anxiety (Haas, B.W., Reiss, A. (2012). Early development in WS is marked by low birth weight, gastroesophageal reflux, and ineffective breast feeding (Tsai et al., 2008). Most children exhibit low IQ levels, atypical verbal development, suffer from cardiovascular abnormalities and show facial dysmorphies which may not be evident until 1.5-2 years of age. Motor development delay is observed in both children and adults (Tsai et al., 2008). Notable interest in face processing and increased sociability is observed early in life. Studies have found that infants (8-43 months) with WS showed greater gaze duration at their mothers than the control group did. Moreover, individuals with WS spent the same time looking at a stranger, suggesting high sociability and enhanced affiliative drive (Mervis et al., 2003). Children with WS (ages 8-13) commented more frequently on peripheral features such as earrings or other physical traits than did controls which tend to comment on typical features such as eyes and mouth. Interestingly, it has been noted that in individuals with WS concentration on peripheral features declines with age (Martens et al., 2009).
Williams syndrome is coupled with abnormal functions of brain regions underlying mechanisms involved in emotion and face processing. One of the mostly hypothesized brain region involved in neural network is the amygdala. Amygdala is an almond-shaped nuclei located deep inside of the medial temporal lobe (Stefanacci, L., Amaral, D.G., 2002) and plays a crucial role in emotion recognition and facial expressions (Capitao et al., 2011a), fear (Haas et al. 2010a), approachability (Martens et al., 2009), social/ non-social related stimuli (Thornton-Wells et al., (2011) and hypersociability (Capitao et al.2011b). Magnetic resonance imaging (MRI) studies have demonstrated a relative increase in total intracranial amygdala volume in individuals with WS (Capitao et al., 2011b). In addition, the mean right and left amygdala volumes were reported to be larger in WS compared to controls (Martens et al., 2009). Moreover, Martens et al., (2009) reported a relationship between the right amygdala volume and approachability ratings when pictures of “positive” faces were shown to the individuals with WS. This evidence is consistent with the results obtained by Haas et al., (2009b) and Meyer-Lindenberg, et.al., (2005). However, in the study by Haas et al., (2009b) no significant amygdala activation to negative stimuli was observed in WS individuals as compared to the control group who demonstrated an increased activity in the right amygdala to fearful social stimuli.Conversely, Martens et al.(2009) noted predominantly positive correlation between increased amygdala volume and “negative” faces in individuals with WS, which is incongruent with the results obtained by Haas et al., (2009b). Furthermore, Thornton-Wells et al., (2011) asserted that when viewing neutral face stimuli, individuals with WS had an increased amygdala response and were more likely to perceive neutral faces as happy expressions, implying social positivity attitude in WS. These studies suggest that individuals with WS have an atypical amygdala structure and function which underline possible explanations of increased sociability in people with WS.
Individuals with WS tend to show high approachability and low social inhibition levels. A feasible explication of extreme sociability behavior can be related to non-social fear or lack of it. For example, Thornton-Wells et al., (2011) reported higher left amygdala blood oxygen level dependent (BOLD) responses in individuals with WS when viewing fear non-social stimuli. Conversely, when viewing fear social stimuli, WS individuals did not show smaller amygdala BOLD responses as expected in fact, they showed an increased BOLD response to fear social images. This contradicts with the results obtained from Haas et al.,(2009b), who observed attenuated BOLD amygdala responses to fear faces. The inconsistency of these results might be due to the experimental design differences. In Thornton-Wells et al., (2011) experiment a block design with passive viewing was used, whereas in Haas et al., (2009b) event-related design which required a motor response was used.
Amygdala response is crucial for avoidance behavior (Meyer-Lindenberg et al., 2005) therefore, abnormal activation of amygdala to fear faces may contribute to social disinhibition and reduced fear of strangers. WS individuals had trouble recognizing sad and scared emotions (Capitao et al.,2011a). Interestingly, WS individuals identified angry facial emotions the same as their matched mental and chronological controls, implying that they were able to associate angry faces with a potential social threat (Capitao et al., 2011a). This finding gave raise to a hypothesis that people with WS are actually able to distinguish between approachable and non approachable people, but they cannot integrate this information and act accordingly to their social knowledge. In another study, Haas et al., (2009a) described social fearlessness and demonstrated that individuals with WS had an increased tendency to approach strangers. Less left amygdala response to fear stimuli was observed thus, suggesting a model for social fearlessness in WS. Accordingly, lateralization of amygdala function was ascribed to the left. Conflicting with the study done by Martens et al., (2009) between amygdala structure and approachability, lateralization of amygdala structure was attributed to the right. The inconsistency of the results suggests that lateralization of amygdala may account for both structure and function. Abnormalities in the amygdala relate to a failure in recognizing potential threat in the environment and therefore, acquiring trustworthiness and approachability of unfamiliar strangers (Martens et al. 2009). Together, these findings highlight that abnormal social behavior and decreased fear to approach strangers may be proportional to the amygdala structure and function. Atypical function of the amygdala may result from a disrupted orbitofrontal cortex (OFC) which is activated differently and is functionally disconnected from the amygdala in individuals with WS (Meyer-Lindenberg et al. 2005). It has been noted that both medial prefrontal cortex (MPFC) and OFC are interrelated with both the amygdala and dorsolateral prefrontal cortex (DLPFC) and play a crucial role in regulation of amygdala (Meyer-Lindenberg et al. 2005). Meyer-Lindenberg and colleagues (2005) showed that individuals with WS failed to activate OFC region in response to fear faces, whereas both MPFC and DLPFC were equally responsive during face tasks. Additionally, path analyses demonstrated a functional disconnect between OFC with either amygdala or DLPFC and found that OFC did not participate in regulatory interactions with amygdala in individuals with WS in response to threatening faces. Controls on the other hand showed a strong connection between the OFC and amygdala. Together these findings may propose that disruption in amygdala-prefrontal circuitry in individuals with WS may potentially be the evidence for atypical social processing. Bidirectional pathways linking the amygdala and orbitofrontal cortex may underline the experience of emotions (Ghashghaei, H.T., Barbas, H., 2002). Axons from the OFC project densely onto the amygdala (Stefanacci, L., Amaral, D.G., 2002) and synapse inside GABAergic nuclei underlying that OFC areas execute control on the internal processing of the amygdala (Ghashghaei, H.T., Barbas, H., 2002). In the recent study by Avery S.N, Thornton-Wells T.A (2011) scientists suggested that unsuccessful inhibition of the amygdala by OFC may attribute to amygdala hyperactivity. Likewise, they implied that structural abnormality of myelinated axons may be a plausible mechanism leading to anomalies in prefrontal-amygdala inhibitory pathways in WS individuals. The results showed reduced white matter integrity in the prefrontal and amygdala regions in individuals with WS compared to controls. This finding could possibly explain .the OFC-amygdala functional disconnect previously described by (Meyer-Lindenberg et al., 2005). In addition, white matter integrity deficits may underline a neural mechanism for the excessive amygdala hyperactivity and elevated non-social fear in WS individuals (Avery S.N, Thornton-.Wells T.A 2011). However, very little research has been done regarding this matter and due to limitations such as small sample size these results should be interpreted with vigilance. Causes of amygdala hyperfunction are in part genetic, resulting from a deletion of certain genes. Individuals with WS exhibited variations in fMRI and BOLD responses and increased tendency to approach strangers indicating abnormalities in amygdala structure and function. Neural mechanisms underlining atypical processes are associated with white matter integrity deficit and a failure of OFC to inhibit amygdala responses during non-social fear behavioral tasks. Together these findings contribute to hypersocial behavior model in WS individuals. However, studies produce contradicting evidence and further research needs to be conducted to link amygdala structure, function, the role of OFC and white matter integrity deficits.
References
Avery, S.N., Thorton-Wells, T.A., Anderson, A.W., Urbano Blackford, J (2011).White matter integrity deficits in prefrontal–amygdala pathways in Williams syndrome, NeuroImage 59 887-894
Capitao, L., Sampaio, A., Sampaio, C., Fernandez, M., Sousa, N., Pinheiro, A., Goncalves, O.F (2011a)Williams syndrome hypersociability: A neuropsychological study of the amygdala and prefrontal cortex hypothesis.
Research in Developmental Disabilities. 32, 1169-1179
Capitao, L., Sampaio, A., Sampaio, C., Vasconcelos, C., Fernandez, M., Garayzabal, E., Shenton, M. E., and Goncalves, O. F. (2011b) MRI amygdala volume in Williams Syndrome. Research in Developmental Disabilities. 32, 2767–2772
Ghashghaei, H.T., Barbas, H., (2002). Pathways for emotion: interactions of prefrontal and anterior temporal pathways in the amygdala of the rhesus monkey. Neuroscience
115, 1261–1279.
Haas, B. W., Hoeft, F., Searcy, Y. M., Mills, D., Bellugi, U., and Reiss, A. (2009a). Individual differences in social behavior predict amygdala response to fearful facial expressions in Williams syndrome. Neuropsychologia 48, 1283–1288.
Haas, B. W., Mills, D., Yam, A., Hoeft, F., Bellugi, U., and Reiss, A. (2009b). Genetic Influences on Sociability: Heightened Amygdala Reactivity and Event-Related Response to Positive Social Stimuli in Williams Syndrome The Journal of Neuroscience 29(4),
1132-1139.
Haas, B.W., Reiss, A. (2012). Social brain development in Williams syndrome: the current status and directions for future research, Frontiers in Psychology 3 (186), 1-13
Martens, M. A., Wilson, S. J., Dudgeon, P., and Reutens, D. C. (2009).
Approachability and the amygdala: insights from Williams syndrome. Neuropsychologia 47, 2446–2453.
Mervis, C. B., Morris, C. A., KleinTasman, B. P., Bertrand, J., Kwitny, S., Appelbaum, L. G., and Rice, C. E. (2003). Attentional characteristics of infants and toddlers with Williams syndrome during triadic interactions. Dev. Neuropsychol. 23,
243–268
Meyer-Lindenberg, A., Hariri, A.R., Munoz, K.E., Mervis, C.B., Mattay, V.S., Morris, C.A.,
Berman, K.F., (2005). Neural correlates of genetically abnormal social cognition in
Williams syndrome. Nature Neuroscience 8, 991–993.
Meyer-Lindenberg, A, Mervis, CB, Berman, KF., (2006). Neural mechanisms in Williams syndrome: a unique window to genetic influences on cognition and behaviour. Nature Neuroscience 7, 380–393
Stefanacci, L., Amaral, D.G., (2002). Some observations on cortical inputs to the macaque monkey amygdala: an anterograde tracing study. J. Comp. Neurol. 451, 301–323.
Thorton-Wells T.A., Avery S.N., Urbano-Blackford J. (2011). Using novel control groups to dissect the amygdala’s role in Williams syndrome. Developmental Cognitive Neuroscience 1, 295-304
Tsai, S.W., Wu, S.K., Liou, Y.M., Shu, S.G., (2008). Early development in Williams Syndrome. Pediatrics International 50, 221–224
Williams’s JCP, Barratt-Boyes BG, Lowe JB (1961). Supravalvular aortic stenosis. Circulation
24, 1311–1318.