Amygdala is the organ in the limbic system (inner mind) —though a tiny little one is significantly responsible for our emotions which falls in the bracket of implicit memories.
Few things upset creationists more than evidence that they are not only apes and share a common ancestor with the other African apes, but that they also share a common ancestor even with non-mammals such as reptiles, and yet, as the American evolutionary biologist, Theodosius Dobzhansky reminds us, nothing in biology makes sense without the Theory of Evolution (TOE).
And one thing that does make sense is how the human brain is the result of an evolutionary process with ancestry in those common ancestors, including lizards.
A second thing that creationists who have deluded themselves into believing that mainstream biomedical scientists are giving up on the TOE and adopting the childish notion of intelligent design, will find distressing, is the news that the team who did this piece of research are firmly convinced that the structure of our brain and the way it works is the result of evolution, not magic.
The third thing is how this explains empathy, of which creationists often feign ignorance, claiming they get their sense of right and wrong from their invisible friend and have a handbook to tell them how to behave. The curious belief that even influenced supposed Christian intellectual 'giants' such as the smugly self-satisfied, C.S. Lewis, is despite the fact that one of the Golden Rules of human society, that even the founder of Christianity, Jesus, allegedly told his followers to apply - "Do unto others what you would they do unto you" or words to that effect, depend entirely on having the empathetic ability to know what someone else would want.
The research explains how this ability in humans comes from an ancestral ability to read social signals and form relationships, including an understanding of social hierarchies, possessed even by lizards.
What information do you have on the amygdala, it's evolution and the role it plays in humans? The Amygdala: An OverviewThe research team, led by Assistant Professor Rodrigo Braga of Northwestern University, recently published their findings in Science Advances. Their research is explained in a Northwestern University Press release:
Structure and Location The amygdala is a small, almond-shaped cluster of nuclei located deep within the temporal lobes of the brain, forming part of the limbic system. It plays a crucial role in emotional processing, memory formation, and behaviour regulation.
Evolution of the Amygdala
- Ancient Origins
- The amygdala is considered an evolutionarily ancient brain structure, present in all vertebrates. It originates from the basal ganglia, part of the early vertebrate brain.
- In ancestral vertebrates, the amygdala was integral for survival behaviours, such as responding to threats, finding food, and mating.
- Development in Mammals
- In mammals, the amygdala has expanded and diversified, acquiring additional functions, particularly in processing complex emotional and social behaviours.
- Its connections with the neocortex—an area responsible for higher-order functions—allow integration of emotions with cognition.
- Human Amygdala
- The human amygdala is highly developed, reflecting our need for advanced emotional and social processing.
- It is particularly important for interpreting social cues, such as facial expressions, and is involved in nuanced emotional experiences like empathy and fear modulation.
Role of the Amygdala in Humans
- Emotion Processing
- The amygdala is best known for its role in generating and regulating emotions, especially fear and aggression.
- It evaluates sensory inputs to assess threats and triggers appropriate responses, such as fight-or-flight behaviours.
- Memory Formation
- It influences how memories are stored by enhancing retention of emotionally significant events.
- The amygdala interacts with the hippocampus, helping to attach emotional significance to memories, such as remembering joyful or traumatic experiences.
- Decision-Making and Behaviour
- Plays a role in risk assessment and decision-making, particularly when emotions are involved.
- It can influence impulsive behaviours, especially under stress or fear.
- Social Interactions
- Critical for interpreting social signals like facial expressions and body language.
- It helps regulate responses to social rewards and punishments, affecting social bonding and trust.
- Mental Health
- Dysfunctions in the amygdala are implicated in several mental health conditions, such as:
- Anxiety disorders: Overactivation leads to excessive fear responses.
- Depression: Altered amygdala activity is linked with emotional dysregulation.
- Autism Spectrum Disorder: Differences in amygdala structure and function may contribute to social processing difficulties.
Evolutionary Implications
The evolution of the amygdala underscores its critical role in survival and adaptation. As a highly conserved structure, it highlights how basic survival functions have been retained and elaborated upon in more complex organisms, culminating in humans' ability to process intricate emotional and social information. This evolutionary trajectory reflects the increasing importance of emotion and social behaviour in survival and reproduction, particularly in species with complex social systems like primates.
Wonder what others are thinking? It’s your ‘lizard brain’ talking
New understanding of brain communication could one day help treat anxiety and depression
We’ve all been there. Moments after leaving a party, your brain is suddenly filled with worries about what others were thinking. “Did they think I talked too much?” “Did my joke offend them?” “Were they having a good time?”
In a new Northwestern Medicine study published in Science Advances, scientists sought to better understand how humans became so skilled at thinking about what’s happening in other peoples’ minds. The findings could have implications for one day treating psychiatric conditions such as anxiety and depression.
background: Evolutionary timelines
We spend a lot of time wondering, ‘What is that person feeling, thinking? Did I say something to upset them? The parts of the brain that allow us to do this are in regions of the human brain that have expanded recently in our evolution, and that implies that it’s a recently developed process. In essence, you’re putting yourself in someone else’s mind and making inferences about what that person is thinking when you cannot really know.
Assistant Professor Rodrigo Braga, senior author.
Department of Neurology
Northwestern University Feinberg School of Medicine
Chicago, IL, USA.
The study found the more recently expanded parts of the human brain that support social interactions — called the social cognitive network — are connected to and in constant communication with a more ancient part of the brain called the amygdala.
The amygdala’s role
Humans’ common ancestor with lizards likely also had an amygdala, which is why it’s often referred to as our “lizard brain.” It’s typically associated with detecting threats and processing fear. A classic example of the amygdala in action is someone’s physiological and emotional response to seeing a snake: startled body, racing heart, sweaty palms. But the amygdala also does other things, Braga said.
For instance, the amygdala is responsible for social behaviours like parenting, mating, aggression and the navigation of social-dominance hierarchies. Previous studies have found co-activation of the amygdala and social cognitive network, but our study is novel because it shows the communication is always happening.
Assistant Professor Rodrigo Braga.
Within the amygdala, there’s a specific part called the medial nucleus that is very important for social behaviours. This study was the first to show the amygdala’s medial nucleus is connected to newly evolved social cognitive network regions, which are involved in thinking about other people. This link to the amygdala likely helps shape the function of the social cognitive network by giving it access to the amygdala’s role in processing emotionally important content.
High-resolution brain scans were key
The researchers were able to make their discovery thanks to functional magnetic resonance imaging (fMRI), a noninvasive brain-imaging technique that measures activity by detecting changes in blood oxygen levels.
A collaborator at the University of Minnesota and co-author on the study, Kendrick Kay, provided the researchers with high-resolution fMRI data from six study participants as part of the Natural Scenes Dataset. These high-resolution scans enabled the scientists to see new details of the social cognitive network. The researchers then supplemented this with data collected at Northwestern’s Center for Translational Imaging, where participants performed tasks targeting social cognitive processes.
We were able to identify network regions we weren’t able to see before. That’s something that had been underappreciated before our study, and we were able to get at that because we had such high-resolution data.
Donnisa Edmonds, corresponding author
Department of Neurology
Northwestern University Feinberg School of Medicine
Chicago, IL, USA.
Potential treatment of anxiety, depression
Both anxiety and depression involve amygdala hyperactivity, which can contribute to excessive emotional responses and impaired emotional regulation, Edmonds said. Currently, someone with either condition could receive deep brain stimulation for treatment, but this means having an invasive, surgical procedure. Now, with this study’s findings, a much less-invasive procedure, transcranial magnetic stimulation (TMS), might be able to use knowledge about this brain connection to target the amygdala by stimulating regions of the social cognitive network which sit on the brain surface. While researchers don’t yet know if this would have a beneficial effect, it presents an exciting future avenue of investigation, Braga said.
Through this knowledge that the amygdala is connected to other brain regions — potentially some that are closer to the skull, which is an easier region to target — that means people who do TMS could target the amygdala instead by targeting these other regions.
Donnisa Edmonds
The study is titled, “The human social cognitive network contains multiple regions within the amygdala.” Other Northwestern co-authors include Christina Zelano, Joseph J. Salvo, Nathan Anderson, Maya Lakshman and Qiaohan Yang.
There is a lot here to have creationists reaching for their playbook to see how to dismiss it: there is the evidence of common ancestry with a pre-mammalian vertebrate, the neurophysiological explanation for innate morality in the form of empathy and social awareness and there is the complete dependence on the Theory of Evolution to explain the results with no hint of the scientists turning to a childish superstition like creationism for a better answer. Probably the most effective way for a creationist to cope will be to simply ignore the evidence in the hope that it'll go away.Abstract
Reasoning about someone’s thoughts and intentions—i.e., forming a “theory of mind”—is a core aspect of social cognition and relies on association areas of the brain that have expanded disproportionately in the human lineage. We recently showed that these association zones comprise parallel distributed networks that, despite occupying adjacent and interdigitated regions, serve dissociable functions. One network is selectively recruited by social cognitive processes. What circuit properties differentiate these parallel networks? Here, we show that social cognitive association areas are intrinsically and selectively connected to anterior regions of the medial temporal lobe that are implicated in emotional learning and social behaviors, including the amygdala at or near the basolateral complex and medial nucleus. The results suggest that social cognitive functions emerge through coordinated activity between internal circuits of the amygdala and a broader distributed association network, and indicate the medial nucleus may play an important role in social cognition in humans.
INTRODUCTION
The ability to reason about another person’s intentions and beliefs—i.e., to form a “theory of mind” (ToM)—is an important aspect of social cognition that assists the navigation of social interactions (1). In the human brain, tasks targeting ToM activate a set of association regions that are late to mature and are disproportionately expanded in the hominin lineage (2–5), supporting that the primate brain may have expanded following evolutionary pressures associated with living in complex social groups (6). In addition, evidence supports that evolutionarily ancient structures, such as the amygdala and related medial temporal lobe (MTL) circuitry, are key controllers of social behaviors (7–10). Here, we show that these expanded cortical social cognitive regions and evolutionarily older MTL structures form an intrinsically connected network supporting ToM in humans.
Brain regions involved in ToM can be examined by studying changes in the blood oxygenation level–dependent (BOLD) signal (11, 12) during “false belief” and “emotional pain” tasks. In the false belief task (13, 14), participants answer questions from the perspective of someone who holds a mistaken belief (e.g., Sally believes a cherry cake tastes of strawberries because it was mislabeled). In the emotional pain task, participants rate the pain a protagonist may feel following an emotionally painful event (e.g., the loss of a family pet) (15–17). Both tasks require thinking about someone else’s thoughts and activate a network of cortical regions that includes the temporoparietal junction, the ventromedial and dorsomedial prefrontal cortex, the lateral temporal cortex, and the posteromedial cortex (16, 18–20). However, early observations noted that these same regions were recruited during other tasks (21–24), including those involving not only social interactions without an explicit mentalizing component (25, 26) but also tasks targeting more diverse processes such as autobiographical memory (27), self-oriented thinking (23, 24, 28–30), and “episodic projection” (EP; i.e., thinking about the past or future) (31–33). The same set of association regions was also conceptualized as the canonical “default network” (DN) (21, 34, 35), which is definable from resting-state correlations of the BOLD signal (i.e., functional connectivity or FC) (36, 37), exhibits connectivity to the MTL (21, 37–39), and shows increased activity during passive “rest” periods between active tasks (40). This overlap between ToM, the DN, and other memory-related processes led to the idea that the DN plays a domain-general role in introspection and mind wandering, which tends to include thoughts about others (31, 41–49) [e.g., see the twelfth figure in Buckner et al. (21) and first figure in Mars et al. (22)].
An alternative view is that the canonical DN appears to be domain generalized because it is a coarse (i.e., blurry) estimate of finer-grained, domain-specialized networks. For instance, it was noted that, even in group-averaged estimates, which blur over individual differences (50–53), there are hints of substructure within the canonical DN (43, 54–61); ToM tasks tend to activate a more anterior region of the inferior parietal lobe at or near the temporoparietal junction, while EP tasks recruit more posterior regions (57, 59, 60). Similarly, ToM tasks typically recruit dorsal posteromedial regions at or near the posterior cingulate cortex, while EP tasks typically recruit more ventral regions at or near the retrosplenial cortex. These distinctions presaged findings from finer-grained, individual-focused analyses. Within individuals, separable posteromedial regions were found to be active when participants were asked to think about relationships between people or places (20, 62–65). This supports a separation between social and episodic processes within the DN and suggests that EP-related activity may be related to spatial mnemonic processes or mental “scene construction” (49, 66, 67). In these examples, social cognition was again located in more dorsal posteromedial regions, whereas EP-related activity was located in more ventral regions, matching the distinctions noted in group-averaged data. These findings indicate that the convergence of functions on a canonical DN may have been due to blurring across distinct, adjacent regions that separately support social and episodic functions (24).
Fig. 1. High-resolution FC separates DN-A and DN-B using both surface-based and volume-based approaches.
(Left) Networks defined on surface-projected data for each subject (S1 to S4, S6, and S7) using data-driven clustering (k = 14) (116). The surface visualization allows easier observation of the cortical sheet but excludes medial temporal structures. The networks were therefore identified independently in the volume (Right) and projected to the surface for comparison between methods. The volume-defined maps [Fisher’s r-to-z transformed Pearson’s product-moment correlations; z(r)] were thresholded at r > 0.3, binarized, and overlaid to display where DN-A (blue) and DN-B (yellow) are distinct or overlap (orange). Hollow circles indicate approximate locations of seeds selected in the volume that targeted DN-A (A) and DN-B (B).
Fig. 3. DN-B contains distinct regions in the anterior MTL, including the amygdala, EC, and potentially subiculum.
Sagittal views of the volume-based FC maps of DN-A (Left) and DN-B (Middle) from an example subject (S2), with the mean BOLD image as an underlay. The correlation maps were thresholded at 0.2 and binarized to display an overlap map (Right). The top row shows the midline to display the characteristic medial distinctions between the networks. The second row shows a slice along the MTL, where interdigitated regions of DN-A and DN-B can be seen along the long axis, with DN-B displaying regions in the anterior MTL. The dashed boxes indicate the location of the zoom-in shown in the lower two rows. The lowest row shows the T1 image as the underlay for better appreciation of the anatomy. Arrows indicate the approximate locations of the amygdala (a), EC (e), subiculum (s), and parahippocampal cortex (p) and are consistent between panels to allow comparison. The dashed vertical lines indicate the location of the coronal slices shown in Fig. 4. z(r), Fisher’s r-to-z transformed Pearson’s product-moment correlations. Numbers in each panel correspond to MNI slice coordinates.
Fig. 5. Individualized amygdala segmentation confirms that regions of DN-B are located in or near the BLA.
(Top row) Example subject’s (S1) T1 and mean BOLD images, zoomed into the right amygdala, showing estimates of the amygdala nuclei from an automated, individualized segmentation (127) (see fig. S9 for other subjects). The remaining rows display the amygdala segmentation in each subject (S1 to S4, S6, and S7) around MNI y = −6 to −9, along with the FC estimates of DN-A (Middle Right) and DN-B (Middle Left), and their overlap (Right). (Left) Full coronal slice with the map of DN-B, with a box indicating the zoom-in location. White arrows indicate putative regions of DN-B, which did not overlap with DN-A. In each subject, the regions of DN-B appeared to overlap most prominently with the basal (BA) or accessory basal nucleus (AB) in each subject. Evidence for a distinct region can also be seen in ventral portions of the lateral nucleus (LA) in some subjects. Furthermore, DN-B regions also extended dorsomedially beyond the BLA (see S1 to S3) but notably did not overlap with the CeA. Other abbreviations refer to cortico-amygdaloid (Acot), cortical (Cort), and paralaminar (PL) nuclei.
Fig. 7. Seeds targeted to medial amygdala (MeA) selectively reproduce distributed network DN-B.
(Left) Zoom-in on a sagittal view of the MTL showing each subject’s T1 and overlap map (similar to Fig. 3). FC maps (Right) (see color bar) from seeds targeting the MeA region of DN-B in each individual (white circles) recapitulated the distributed pattern of DN-B (see black outlines denoting surface-defined DN-B shown in Fig. 1), despite the amygdala showing reduced SNR (fig. S1). The strength of correlation varies across individuals (e.g., compare S7 with S1), which could be due to many factors, including data quality, signal dropout, the size of the amygdala region being targeted, and accuracy of seed selection.
Fig. 2. Functional imaging at 3T in eight additional individuals (DBNO_01 to DBNO_08) confirms functional dissociation between DN-A and DN-B.
Black borders show FC estimates of DN-A (Left) and DN-B (Right) from data-driven clustering (from fig. S2). The same participants provided data during tasks targeting ToM and EP. The ToM task contrasts revealed increased activity in multiple regions that overlapped selectively with the boundaries of DN-B. In contrast, the scene construction contrast which targeted EP revealed that, while participants imagined scenes, increased activity was evident in regions that overlapped with DN-A. The results confirm (20) that network DN-B is selectively recruited during social cognitive processes and is functionally dissociated from DN-A.
Fig. 4. Basolateral and medial amygdala regions of DN-B are bilateral and replicate across participants.
Volume-based FC maps of DN-B are shown in coronal slices. Numbers refer to the MNI coordinate of each slice. (Left) Views around y = −6 to −9, where five of six subjects (exception: S6) displayed bilateral regions putatively in the basolateral amygdala. (Right) Slices around y = −3 to −5, where, in all six subjects, a distinct set of bilateral (three of six) or unilateral (three of six) regions could be seen putatively near the medial amygdala (Fig. 6). The white solid line in S1, S4, and S7 denotes that left and right hemispheres are from different slices. Arrows denote putative DN-B regions that were distinct from DN-A (see Figs. 5 and 6 for overlap map at these same slices and replications in figs. S6 and S7).
Fig. 6. Hand-drawn segmentation confirms that DN-B regions are in or near the MeA of the amygdala.
The MeA was hand drawn by an expert blinded to the network maps, following Noto et al. (128) and Mai et al. (130). All subjects displayed a region of DN-B that partially overlapped or was adjacent to the estimate of the MeA and that did not overlap with DN-A (see overlap map). Figure formatted according to Fig. 5.
Fig. 8. Two distributed cortical networks are interdigitated along the long axis of the MTL.
Circles indicate seeds that were hand selected in two subjects [S2 (Left) and S4 (Right)] to target DN-A and DN-B along the MTL, namely, within the (A) parahippocampal cortex (for DN-A), (B) subiculum (DN-B), (C) EC (DN-B), (D) subiculum (DN-A), and (E) basolateral amygdala (DN-B). Filled-in circles indicate seeds selected from the slice shown, and hollow circles indicate seeds selected in adjacent or nearby slices. Surface renderings underneath show the FC maps (color bar) from the corresponding seeds, with a black border indicating network DN-B as defined in the surface (Fig. 1). In both individuals, seeds A and D reproduced network DN-A, while seeds B, C, and E reproduced network DN-B, suggesting that DN-A and DN-B are interdigitated along the MTL. Note that the subiculum region of DN-B (seed B) was more posterior than the subiculum region of DN-A (seed D).
Fig. 9. Group-averaged resting-state FC maps from the UK Biobank reveal MeA and BLA regions of the DN-B at lower thresholds.
Sagittal and coronal views show “component 1” from an ICA and 25 dimensions of data from 4181 UK Biobank participants (131). At the default threshold (z = 5) (Top row), the network exhibits typical characteristics of DN-B including regions in the posteromedial cortex (PMC), medial PFC (mPFC), and dorsomedial PFC (dmPFC). At a lower threshold (z = 3) (Lower row), the network additionally includes amygdala regions at the MeA and BLA along with a region in the subiculum (SUB).Donnisa Edmonds et al.
The human social cognitive network contains multiple regions within the amygdala. Sci. Adv. 10, eadp0453 (2024). DOI:10.1126/sciadv.adp0453
Copyright: © 2024 The authors.
Published by American Society for the Advancement of Science. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
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