Von Economo Neurons and Self-Awareness

Von Economo Neurons and Self-Awareness Joshua McCosker Von Economo neurons (VENs) are large bipolar neurons found in the anterior cingulate cortex (ACC), frontoinsular cortex (FI) and dorsolateral prefrontal area (DLPA) in the brains of humans, and to a lesser extent, the great apes, several cetaceans and elephants. It is believed that they arose independently within these species due to evolutionary pressure that required the rapid transmission and cognitive processing of social information in animals with large highly convoluted brains and complex social behaviours (Hakeem et al., 2009). Research has suggestedsuggests that the evolution of these neurons underlie the emergence of intuition, higher emotional cognitive functions and self-referential processes. This suggests an intriguing connection with the subjective conscious experience and self-conscious awareness (Critchley Seth, 2012). To investigate this connection between VENs and self-awareness it is necessary to examine the known behavioural functions of the ACC and FI, along w ith the evolution of these structures and the integration with this novel class of neuron. Furthermore, the higher social functions attributed to VENs and how these are related to awareness of consciousness self will be discussed in light of research that shows a correlation between the degeneration of VENs in several neuro-psychiatric disorders that leads to devastating deficits in conscious awareness and social skills (Butti, Santos, Uppal, Hof, 2013). The ACC and FI are found in the paralimbic cortex (also known as mesocortex) of the mammalian brain and represents a relatively ancient region that has recently gone through a period of evolutionary adaptive changes in humans and is directly connected to limbic structures while providing a transition to higher neocortical regions (Brà ¼ne et al., 2010; William W. Seeley et al., 2006). These paralimbic structures show increased connectivity with the hippocampus, amygdala, orbitofrontal cortex and septum; the septum is involved in social memory and the development of trust in humans (Allman, Tetreault, Hakeem, Park, 2011). It is hypothesised that this enhanced connectivity is mediated by VENs that project from the FI and ACC to these structures providing functional integration with of somatosensory input and higher cognitive emotional processes leading to the emergence of intuition, social and self-awareness and the ability to empathise (Allman, Tetreault, Hakeem, Manaye, et al., 201 1; Allman, Tetreault, Hakeem, Park, 2011). AIC as the input sensory region and ACC as the output control region (Craig, 2009; W. W. Seeley et al., 2007). The evolutionary expansion of the cerebral cortex gave rise to the neocortex in mammals leading to a volumetric increase in humans of several-hundred times over that of lower primates (Nimchinsky et al., 1999). However, the types of neurons found within the brain have remained relatively constant (Nimchinsky et al., 1999; William W. Seeley et al., 2006). In 1926 Constantin Von Economo first described the cortical distribution and morphology of a novel class of neuron as being spindle like in form and of unusual length (Butti et al., 2013).. Von Economo neurons are large bipolar projection neurons that are relatively recent on the evolutionary path (Allman, Watson, Tetreault, Hakeem, 2005). They have large axons that bidirectionally connect the ACC to the FI and in turn to other structures of the brain between the limbic cortex and neocortex; suggesting a role in the rapid transmission of sensory information between these structures. Although VENs have been found in the FI and ACC of species other than great apes and homonids the cells are not found in the concentrated clusters that have been described in higher primates (Bauernfeind et al., 2013). It is interesting to note that volumetric studies have shown that the evolutionary expansion in size of the FI in primates is disproportionately greater to overall brain expansion by 36% and the total volume of the FI is about 4 times larger in humans compared to that of the chimpanzee (Bauernfeind et al., 2013). Furthermore, it is known that the vast majority of VENs develop during the first 8 months of life (Allman et al., 2010) . and this coincides with the emergence of stranger anxiety, separation anxiety and increased verbal skills (Hoffnung et al., 2013). These studies support the suggestion that the FI and ACC are intricately involved in enhancing social behaviours through the utilization of subjective emotional states in applying empathy toward others. ReseachResearch hasis showning a relationship between complex social and emotional processes and the advanced cognitive abilities that underlie the ability of self-recognition (Hunter, 2010). The mirror self-recognition test is used to assess self-awareness in animals and was developed by Gordon G. Gallup (1970) during his work with chimpanzees and self-recognition. In humans the ability to recognise the ‘self’ in a mirror image develops between the ages of 18 and 24 months and this coincides with the development of other indicators of social and self-awareness such as the ability to empathise (Hunter, 2010). As previously mentioned there is a rapid development of VENs during the first year of life and this development continues to age 4 when VEN numbers align to those of adult (Allman et al., 2010). The hypothesised role of VENs in higher cognitive functions and self-conscious awareness is supported by research that has shown the involvement of VENs in the pathogenesis of a number of neuropsychiatric and behavioural conditions that are characterised by deficits in emotional and social functioning, the ability to empathise, impairment of affective language and alterations in conscious awareness (Kaufman et al., 2008). Stereological research suggests that these conditions may be due to the failure of VENs to develop normally or the degeneration of these cells within the ACC and FI (Allman et al., 2005; Butti et al., 2013). This is evident in frontotemporal dementia (FTD) where patients present with a severe reduction in social judgement, empathy and the ability to self-monitor leading to sociopathic behaviour (William W. Seeley et al., 2006). In a study conducted by William W. Seeley et al. (2006) it was shown that FTD is characterised by early injury to the ACC and FI involving e arly, severe and selective VENs loss of 74% compared to controls. Similarly, patients with early onset schizophrenia are characterised by a reduced volume of the ACC showing a significant reduction in the density of VENs (Allman et al., 2010; Brà ¼ne et al., 2010). People with schizophrenia show a broad range of impaired social skills characterised by severe disturbance of cognitive processes and self-conscious awareness giving rise to symptoms that include delusions, hallucinations, disorganised thought and speech, disorganised and catatonic behaviour, poverty of speech and lack of, or inappropriate, responses to socio-emotional cues (Nolen-hoeksema, 2007). Recent research has suggested a connection between these VENs containing areas, self-referential processes and the subjective conscious experience of awareness (Allman et al., 2005; Craig, 2009; William W. Seeley et al., 2006). The evolutionary motivation underlying these adaptations may well have been due to the rise of species living in complex social groups that required the rapid intuitive assessment of social interactions and the ability to differentiate between the needs of oneself and those of others and this may have led to the ability to empathise with the emotional state and needs of individuals within the social structure (Allman et al., 2010; Allman, Tetreault, Hakeem, Park, 2011; Hakeem et al., 2009). We shall consider a model of consciousness where the FI serves to integrate bottom-up interoceptive sensory information with top-down predictions and modulations from higher level prefrontal cortical areas and the ACC generating a state of awareness (Gu, Hof, Friston, Fan , 2013). It is hypothesised that VENs mediate a rapid bidirectional feedback between the integration of sensory information in the AIC and the adaptive behavioral responses mediated by the ACC (Allman et al., 2005). Interoception is the integration of somatosensory information leading to a sense of the physiological state of the body, giving rise to a cortical image or representation of self (Craig, 2002, 2009). In humans the interoceptive network is mediated via afferent spinothalamic neurons projecting to the ventromedial nucleus which is significantly larger in humans than other primates; non-primates are unable to experience body feelings in the same manner as humans do due to the lack of the specific afferent spinothalamocortical pathway involved in â€Å"direct interoceptive representation† (Craig, 2002). This homeostatic information is relayed to the anterior insular cortex where there is a re-representation of this interoceptive cortical image and the ACC is involved in the active modulation of the feeling represented by this image in response to cognitive assessment from the orbitofrontal cortex (Allman et al., 2005; Craig, 2002, 2009; William W. Seeley et al., 2006)(Craig, 2002, 2009; Seeley, 2006; Allman, 2005). It is also worth noting that this top-down cognitive assessment could involve conscious internal dialog and suggests the co-evolution of language and consciousness and that we are conscious in a human sense because we have language. Language is not only used for external communication but internally as parts of our thought processes defining our current mental state and by extension is a defining the broader and more complex brain state (Arbib, 2001). The above research shows that VENs are intricately involved in the convergence of somatosensory information via a highly evolved thalamacortical pathway to the paralimbic structure of the AIC in which emerges an integrated cortical image. Bidirectional signaling between between the AIC, ACC and multiple areas of the brain is mediate via VENs and is a contiual feedback loop that assesses and updates this cortical self-image utilising contextual cues derived from the environment and past experiences accessed from long term memory via hippocampal projections. The AIC cortical self-representation is modulated with emotional context and predictive behavioural responses. References Allman, J. M., Tetreault, N. A., Hakeem, A. Y., Manaye, K. F., Semendeferi, K., Erwin, J. M., . . . Hof, P. R. (2010). The von Economo neurons in frontoinsular and anterior cingulate cortex in great apes and humans. Brain Structure and Function, 214(5-6), 495-517. doi: http://dx.doi.org/10.1007/s00429-010-0254-0 Allman, J. M., Tetreault, N. A., Hakeem, A. Y., Manaye, K. F., Semendeferi, K., Erwin, J. M., . . . Hof, P. R. (2011). The von Economo neurons in the frontoinsular and anterior cingulate cortex. 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