Distinguishing Partisan and Extremist Brains?: Research Paths toward Neural Signatures of Violent Radicalism

Abstract

Neuroimaging of political ideologies (left-wing vs. right-wing; conservatism vs. liberalism), unveiled brain systems for mediating the cognitive and affective inclinations of partisanship. Brain networks related to deliberation and cognitive control, as well as those processing subjective values and social norms, were mainly involved. Correlational links from normative people were corroborated by brain lesions and focal transcranial stimulation techniques. Neuroimaging studies with extremists ready to endorse violent actions are scarce and do not provide fully concordant maps with those coming from people with strong partisanship allegiances. The present review discusses the advances made in the description of the neural systems that mediate both ordinary partisanship (the “partisan brain”), and radicalized extremism prone to violence (the “extremist brain”), signaling concomitances and differences. Further advances might come from unveiling distinctive interactions between prefrontal cortex areas with other cortical and subcortical regions that may help to outline dedicated maps and modes of operation. Moreover, measuring the hardness of beliefs and the strength of value adscriptions together with cognitive flexibility/rigidity, aggressiveness, ambition, high-risk seeking and other individual traits rooted in psychobiological substrates appear indispensable to distinguish between partisanship alignments and violent extremism proneness.

1. Introduction

Terrorist attacks were a source of enormous apprehension during the inaugural years of the present century, in many Western societies. The sheer brutality and the number of casualties provoked by extremist violent actions at the heart of major conurbations and big capital cities justified citizen’s worries and the concerted actions of States to try to prevent these attacks. For years, counter-terrorism measures deployed by armed forces, police branches, and intelligence agencies against extremist groups and networks (mostly heralding versions of islamic yihad), were at the forefront of political scenarios. The living routines of common citizens were notoriously affected particularly when moving through airports, train stations, customs borders, and tourist hotspots. But after the defeat and dismantling of ISIS strongholds in the Middle East and the dispersal of Al-Quaida granular remnants away from the region, the threat of terrorism subdued to a large degree. The detailed data collected by the Global Terrorism Database (GTD: https://www.start.umd.edu/gtd), confirm a robust decrease in the number of terror attacks in Europe, North and South America, Middle East, and North Africa, as well as on the global Worldwide figures, during the last decade.

Improved methods of surveillance of extremist groups and the adoption of harsh military counter-terrorism tactics and prompt police-based procedures to coagulate attempts of further violent operations greatly enhanced the efforts of terrorism prevention. Efforts were perhaps helped by two external and unexpected events: 1. the eclosion of a catastrophic and long global pandemic (Covid-19), in January 2020 and 2. the eruption of a major European war, between Russia and Ucrania, which has been evolving since February 2022. Both events dramatically shifted the focus and priorities of the defensive measures taken by the States and the general worries of the citizenry.

The scholarly studies on terrorism flourished during the period that extremist actions attained peaks of lethality and captured the world’s attention, but after two decades of intensive research on all kinds of socioeconomic roots, political facilitators, and psychological attributes and processes plausibly linked to the appearance of the phenomenon, no solid advances have been registered and no consensual positions have been reached on the issue [1, 2, 3].

In this essay I will depart from several assumptions that can be stated in a very simple way: 1. terror attacks are one of the typical tactics used in guerrilla wars or insurgencies; 2. perpetrators are ordinary combatants participating in these conflicts; 3. this applies both to commandos formed by a troupe of fighters and to “lone wolves” who appear to operate on their own; 4. behind these actions there can be clandestine groups operating through loosely connected links or tightly organized and well-trained armies that dominate a specific territory; and 5. these lethal operations always carry the signature of a highly advertised political ideology or a discernible doctrine heralding the goals of such combative coalitions. By keeping on these assumptions, the murderous attacks coming from either rampage shooters or individuals pretending to retribute personal grievances or to acquire high notoriety, can all be excluded from the present analysis. The lethal attacks coming from squads participating in rounds of fights among urban bands or from militias of criminal gangs are equally excluded. I am fully aware that this represents a simplification of the complex and changing varieties of terror attacks but it permits demarcating the phenomenon within the limits of political/doctrinal clashes while agreeing with the encompassing and computational descriptions of terrorism, insurgencies, and warfare [4, 5, 6, 7].

2. The role of “ideology/doctrine” banners

Ideology-motivated missions are the usual envelop heralding the justifications of violent extremist groups that use terror attacks as a tactic to promote and advance their political goals. Political ideology is a set of common beliefs and attitudes that organize views on most social issues. In democracies, in addition to motivate regular voting behavior and structure preferences on a wide range of topics, ideology is behind all sorts of political activism that may include or not the use of violence.

Ideology is usually measured as variations on a unidimensional scale, with liberalism on the left and conservatism on the right. Liberalism promotes equality and social change, while conservatism highlights hierarchy, convention, and tradition. This left-right distinction is the primary way of describing political opinions, though political views cannot be neatly summarized by a single liberal-conservative axis. Libertarians are an obvious example of this misalignment, harboring ‘liberal’ views on social issues but ‘conservative’ views on economic policies. Many studies have converged upon two main dimensions of political ideology. These dual dimensions have repeatedly emerged despite the different labels used to name them [8, 9]. The first dimension, often designated as “economic conservatism” or “social dominance”, predicts positions on issues like taxation, welfare programs, and government public investment. Economic conservatives view the world as a ‘competitive jungle’, in which dominance, inequality, and power imbalances are prevalent. The second dimension, often designated as “social conservatism”, predicts postures on issues like traditional values on sex, education, criminal justice, patriotism, or national security. Social conservatives view the world as threatening, dangerous, and unpredictable. These two-dimensional vectors seem to capture underlying and important psychological phenomena [9].

Variation in political ideology is heritable [10, 11, 12, 13, 14], remains stable over long periods of time [15], and covaries with several basic physiological traits [16, 17, 18, 19, 20, 21, 22]. The two dimensions of ideology are observed across a wide range of cultures [23, 24]. This repetitive pattern of ideological variation across cultures, together with the heritable and mostly stable individual differences suggest that the two dimensions are at least partly grounded in biology. These findings challenged the traditional assumption that ideological variation must be considered the result of historically contingent social, cultural, and environmental factors [9]. Some evolutionary approaches have also derived important insights. This includes work linking social conservatism to negativity bias, disgust sensitivity [22], and adherence to social norms, as well as work linking economic conservatism to upper-body strength [25].

The motivational potency of ideology can be enormous to the point of governing the full spectrum of behavioral outputs of “devoted actors”: dogmatic, fanatized, and highly committed individuals ready to enter into dangerous missions involving maximal risk or even sacrifice their lives [1, 3, 26, 27]. But there are highly variable degrees of “political devotion”. For some people, these strong commitments refer to a readiness to participate in protests, demonstrations, campaigns, and other forms of conventional political activism, whereas for others it means to be ready for harsh fighting against police forces, for harming institutional symbols or buildings or to indulge even on terrorist lethal actions.

3. Sectarian partisanship

With the aim of warning about the dangers for the US democracy of the increasing affective distance between the two main political allegiances, Republicans and Democrats, that had occurred during recent decades, a group of political scientists and social psychologists advanced a definition for the notion of “political sectarianism”, in a joint paper [28]. In their words:

“Political sectarianism consists of three core ingredients: othering - the tendency to view opposing partisans as essentially different or alien to oneself; aversion - the tendency to dislike and distrust opposing partisans; and moralization - the tendency to view opposing partisans as iniquitous. It is the confluence of these ingredients that makes sectarianism so corrosive in the political sphere. Viewing opposing partisans as different, or even as dislikable or immoral, may not be problematic in isolation. But when all three converge, political losses can feel like existential threats that must be averted whatever the cost” [28].

The affective distance separating Democrats and Republicans partisanship carried an ostensible and symmetric aversion and a rising hostility and hate against partisan opponents. Sectarianism was a proper diagnosis for the US political landscape since politics had been reduced to an identity-based struggle against hated and depraved opponents, while shared values and policies on specific issues mattered much less than dominating foes. Three main ingredients had nourished the rise of sectarianism in the US: a widely encompassing and unified identity alignment, along the political allegiance; the persuasive and radicalizing action of both congenial partisan media and social networks; and an increase in the ideological polarization of cultural, economic, and political elites.

They summarized systematic findings showing that sectarianism stimulated political activism and that the surge of US sectarianism was accompanied by a rise in support for violent tactics in political struggles [28]. These trends culminated in the violent assault of the US Capitol Building, in Washington DC, on 6th of January 2021, by an angered mob of D. Trump supporters. They tried to overturn the results of the previous November election by stopping the session of formal nomination of J. Biden as the next President-elect.

Sectarianism or tribalism, however, is hardly a unique US phenomenon since it has been described in all places where political confrontations between highly aligned and entrenched factions grow in intensity to the point of the threshold of inflaming a violent civil conflict [29, 30].

4. Neural systems mediating partisanship and ideological extremism

4.1 Pioneer findings with partisans

The search for plausible neural correlates of political attitudes and beliefs took off when neuroimage studies established that traits related to political preferences (conservatism, individualism, egalitarianism, radicalism), could be linked to particular processing areas within the brain [16, 17, 31, 32, 33, 34, 35]. This was shown for ordinary people and the brain areas more informative were those related to deliberation and cognitive control tasks, and also those weighing affective attachments and subjective values in prefrontal cortex, orbitofrontal cortex, and some subcortical limbic regions. In a study with Vietnam war veterans, Cristofori et al. [36] investigated if traumatic brain lesions could have affected these ideology-linked attitudinal traits. Afflicted veterans were divided into three groups according to lesion location (ventromedial prefrontal cortex-vmPFC; dorsolateral prefrontal cortex-dlPFC and parietal cortex). The results indicated that vmPFC lesions, but not dlPFC ones, decreased radicalism scores. The differences were substantial when compared with veterans with parietal lesions and healthy controls: patients with vmPFC lesions judged radical opinions or behaviors as more acceptable. These findings underscored the role of the vmPFC in appropriately valuing political options and strengthened the notion that vmPFC is a nodal area for assessing many types of values.

In a subsequent study with Vietnam war veterans Zhong et al. [37] confirmed the relevance of both vmPFC and dlPFC brain regions in mediating extreme religious ideas. They found that the areas of prefrontal cortex which are in charge of deliberation and cognitive control (dlPFC, preferently) were predictive of variations in religious fundamentalism. The role of cognitive flexibility was crucial: lower executive skills were accompanied by higher religious dogmatism. Concordant findings were obtained by Nam et al. [32, 33] investigating the links between neuroanatomy and ideological attitudes by comparing brain-lesioned patients with healthy controls. People with frontal lesions held more conservative (less liberal) beliefs than those with anterior temporal lobe lesions or no lesions. Higher damage in dlPFC was associated with enhanced social conservatism. Executive function measures did not predict, however, the relationship between frontal lesions and ideology. Preliminary studies applying focal transcranial electrical stimulation to dlPFC zones obtained transient increases in conservatism attitudes by augmenting the functionality of the region [38]. Overall these findings indicated that PFC areas play a relevant role in mediating political positions and in accentuating conservatism tendencies, in particular.

It is conceivable that the neural correlates primarily related to ideology positions should involve brain regions devoted to deliberation and cognitive flexibility, as they refer to different options on issues that may have important consequences for social organization and ordinary living. However, an Israelian study showed that detectable neural traces of partisanship appear at very early and automatic stages of brain processing [39]. They did fMRI scans of right-wing and left-wing participants watching several political videos just before the hotly contested 2019 elections in Israel. Behavioral results showed consistent differences between left-wing and right-wing participants when appraising and judging video content. Neuroimaging results revealed partisanship-dependent differences in both high-order cortical processing regions and early motor and somatosensory areas, although no such differences appeared while viewing neutral, non-political, videos. The political content was more potent in synchronizing participants with right-wing views, and this synchronization was observed already in primary visual and auditory cortices. These findings suggested that political polarization is not restricted to the functioning of high-order deliberative or affective brain systems, but rather emerges already at the early steps of processing in motor and sensory regions.

Other research has used similar approaches to detect neural synchrony between partisans while contemplating naturalistic political stimulus [40, 41]. They measured the brain activity of committed US partisans (liberal vs. conservative) as they watched video footage of a hot political debate. Although all participants viewed the same videos, brain responses distinguished between liberals and conservatives, reflecting differences in the subjective interpretation of the films. An increased neural synchrony was observed among these partisans on each side of the ideological divide: sharing strong partisan beliefs yielded polarized neural encoding of the debate at the time of perception. This polarized perception was exacerbated by a personality trait: intolerance of uncertainty. Participants less tolerant of uncertainty in daily life had more ideologically polarized brain responses than those who were able to deal with uncertainties in their customary routines and activities. This was observed on both sides of the ideological scenario and the neural signatures of these polarized perceptions predicted subsequent partisanship attitudes outside the laboratory, in agreement with other studies [42].

Bringing between-group economic competitive games to neuroimage sessions with concomitant scans, Yang et al. [43] found that within-group neural synchronization between the right dlPFC and the right temporoparietal junction (rTPJ) underlay intergroup hostility, in young healthy people. During out-group financial attacks, especially, in-group commitment augmented within-group synchronization in both rdlPFC and rTPJ, and within-group rdlPFC synchronization positively correlated with intergroup hostility. The findings also suggested that within-group synchronized reduction in PFC activity might explain how in-group loyalties lead to collective hostility toward outsiders.

4.2 Studies with extremists

Functional neuroimaging studies with Islamic extremists have revealed that they deactivate neural networks associated with deliberation during decisions that involve a high (vs. low) willingness to fight and die for important in-group values [44, 45]. In a research carried out with young male extremists of Magrib origin living in Barcelona region (Spain), sacred values related to cherished Islamic beliefs were associated with increased neural activity in brain regions involved in norm compliance, particularly the left inferior frontal cortex [44]. In a further study with Muslim Pakistani young male radicals living in the same region and who had asserted support for Kashmir fighting groups linked to Al-Qaida, differential brain activities were found when expressing willingness to sacrifice for sacred values in contrast to non-sacred values [46]. Decisions about sacred values involved less activation of pre-frontal brain regions (dlPFC) associated with cognitive executive control. Their asserted willingness to fight and die for these values relied on brain activity within vmPFC areas that appraise subjective values and social rewards. High compared to a low willingness to fight and die was accompanied by a decreased recruitment of brain regions (dlPFC) linked to pondering costs during decision-making. Moreover, the data disclosed negative functional connectivity between these vmPFC and dlPFC regions when processing high versus low willingness to fight and die for an important cause [45]. Thus, rule-bound and quick thinking seems to prevail over deliberation during high-stake decisions involving sacred in-group values in these extremists.

The importance of vmPFC activation in these circumstances agrees well with changes in patterns of activation at this region detected, in ordinary people, while they approved images of politically violent protests in the US [47], and also with measures of imagined aggression [48]. Adjacent prefrontal cortex regions process how situational factors may shape attitudes toward deliberate killing. In laboratory simulations of warfare, ordinary individuals who went through fMRI scans while imagining carrying out unjustified acts of killing (shooting civilians), compared to justified killing (shooting enemy soldiers), showed increased activation in the orbitofrontal cortex (OFC) [49]. The same happened when unjustified shootings were imagined against characters of a Muslim outgroup [50]. In concert, higher activity was detected at OFC together with an enhanced coupling with the amygdala and insula, when individuals viewed harmful behaviors perpetrated by out-group members against in-group fellows [51].

An experiment with far-right voters in Spain and the United States [52] found that these partisans were more likely to share misinformation messages on their social networks than center-right voters, especially when the misinformation was related to sacred values (e.g., postures on immigration). A neuroimaging study with a subsample (N = 36) of these far-right Spanish voters, showed that they presented an increased activity in brain regions implicated in mentalizing tasks and norm compliance while inspecting posts carrying important values. The neural response associated with the intention to disseminate misinformation about protected values was stronger in the dorsomedial prefrontal cortex, the bilateral inferior frontal cortex, and precuneus. This pattern of activation overlapped with the neurofunctional signature of the “theory of mind”. Posts with sacred content also elicited higher functional connectivity between some salience, frontoparietal, and default mode network nodes. These findings cohere with the global pattern of brain activations obtained with ordinary young US individuals (N = 78), from American, Chinese, and Iranian cultures, when they judged the content of real-life stories carrying protected (vs. nonprotected) values [53]. Moreover, In the Spanish study, those messages relevant to sacred (vs. nonsacred) values elicited neural activation in the orbital part of the inferior frontal gyrus rather than the medial zone of this region, in a similar way as obtained with Islamic extremists [52]. The left lateral zones of the orbitofrontal cortex have been described as an important neural spot for social norm compliance, which helps people respond appropriately to the threat of social punishment [54]. These results suggest that two ingredients of political devotion—sacred values and identity fusion with the group—may play a key role in misinformation sharing.

All these findings point toward the role that specified brain systems dedicated mostly to estimation of subjective values and cognitive flexibility/rigidity may play in mediating ideologically driven extremism. These studies opened valuable approaches but their findings should be considered as strictly preliminary for several reasons: procedures to estimate extremism (sacredness, identity fusion, social identity) are rather crude; they typically refer to expression of opinions or intentions, arguably a bit far from proneness to act violently; measures obtained came from restricted samples of some extremist brands; and they used behavioral and neurofunctional methodologies that do not necessarily cohere with other methods to detect plausible signatures for strong partisanship [39, 41, 43].

5. Toward neural signatures for proneness to violent extremism?

People with consistent partisan alignments and preferences are very common. Political extremists with unshakeable partisanship allegiances and heavy activism investments are much less common. And extremists ready to use any kind of violent methods or to indulge even in terror attacks to attain the goals of their combative groups are rather uncommon.

The gradations of intensity in political activism, including the strength of dedication and commitment to the objectives of the side for which they fight [1, 3, 26], must be behind many of these distinctive profiles. But to delimit the underlying psychological vectors of these differences so that they might help to disentangle neural signatures of “partisan brains” compared to “extremist brains”, other operational mechanisms need to be unveiled that can explain such distinctions. Here I suggest some investigative approaches.

5.1 Include temperamental traits

Decety et al. [2] emphasized the need for further and more nuanced research to discern whether the activities and functional connectivities among regions of the prefrontal cortex and subcortical-limbic crucial zones will be able to capture individual differences in proneness to violent extremism. The sketch maps already outlined by the pioneering studies devoted to specify neural circuits mediating extremism, along with their associated molecular (neuromodulatory) cascades, will help to ensure further advances if future explorations would include measures of temperament traits as well as of the different roles played by individuals in extremist groups [4, 5, 55, 56].

Predictably, antisociality/aggressiveness was pointed out as a crucial trait among precursors of violent extremism [2]. It is easy to agree that it seems mandatory to investigate how long-lived propensities to engage in violent and antisocial behavior interact with other trait characteristics measured both at behavioral and biological levels (from gene-based markers and neurohormonal mediators up to brain areas, circuits, and functional systems). Aggressiveness, and particularly, proneness to engage in pro-active, appetitive, or reward-motivated violence [57, 58, 59] will surely emerge as an individual component of combative extremism. Enquiries oriented on this line have a rich and solid body of neurobiological findings to depart from [60, 61, 62].

Moreover, a wide repertoire of neurobiological correlates has been established already for a range of temperament traits potentially linked to different clusters of individuals with proclivity to engage in violent extremism activities. Research on the biological underpinnings of dominance, risk-seeking, dogmatism, parochialism, dishonesty, machiavellianism, and other relevant traits has accrued a good amount of associations with extremism proneness, at different levels of neural analysis. Links that go from gene markers and neurohormones to brain subsystems [4, 5, 30, 47, 56, 63, 64, 65, 66]. These interdependencies have already been used to improve the deployment of provisional but increasingly detailed depictions.

5.2 Beliefs strength

Firmly held beliefs are usually diagnostic of ideological extremism. People endorsing such kinds of beliefs fiercely resist admitting contradictory evidence. In an investigation about the neural systems involved in maintaining belief in the face of counterevidence, 40 young US liberals were presented with arguments that contradicted their strongly held political and non-political views [67]. Challenges to political beliefs produced increased activity in the default mode network (DMN): a set of interconnected brain regions associated with self-representation and disengagement from the external world. High belief resistance was accompanied by increased response in the dorsomedial prefrontal cortex and decreased activity in the orbitofrontal cortex. In addition, participants who changed their minds more showed less activity in the insula and the amygdala when evaluating counterevidence. Increased activation of the DMN during challenges to political beliefs is consistent with the notion that the DMN is recruited to ponder deeply held beliefs. A related fMRI study found that this network was noticeably activated when people read stories that appealed to values that were perceived as strongly held and non-negotiable (“protected values”), compared to reading similar stories devoid of such protected values [53].

One potential path to combine and reconcile these neural correlates of strong beliefs with those mediating partisanship and political extremism, as described before, should explore the processes associated with cognitive rigidity/flexibility. In this regard, focal stimulation procedures applied to specific brain sites showed that they can disrupt, to some degree, firmly held attitudes: “parochialism” [68], “dishonesty-deception” [69, 70], or “fairness-norm compliance” [71]. The transient neural interference induced by these techniques affects regions of the prefrontal cortex dedicated to evaluate options/decisions or DMN areas concerned with self-representation.

6. Conclusion

The decrease in the frequency and lethality of terrorist attacks in many regions of the world, in recent years, as recorded by a thorough global dataset (Global Terrorism Database (GTD: https://www.start.umd.edu/gtd), has not been accompanied by a parallel decrease in the intensity of other forms of intergroup confrontation that sometimes resort to procedures similar to terrorist violence [72]. The wars between cartels in Mexico, for example, have seen tremendous increases in violent episodes, with an overwhelming escalation in the number of incidents and casualties that government police and military interventions failed to stop [73]. This difference in the chronological evolution and in the response to corrective interventions in conflicts grounded on political/doctrinal disputes, on the one hand, compared to those who have motivations aimed at dominating in forceful ways some commercial and financial niches, indicates that these are different phenomena.

On the other hand, surveys carried out on ex-combatants of the Colombian leftist guerrillas who signed up for reintegration programs promoted by the Government, compared with responses obtained from captured combatants, as well as with individuals who demobilized on their own and with others who changed sides and joined the paramilitary groups, it was found that those who joined guerrillas for ideological reasons were the least likely to desert or change sides [74]. These findings strengthen the notion that at the core of motivations inspiring people who join terrorist organizations with political/doctrinal purposes, individual peculiarities related to belief strength and loyalty investments must be crucial. That is a scarcely explored research area [75, 76] where potentially distinctive attributes of “partisan brains” versus “extremist brains” remain to be unveiled and could be singularly informative.

The descriptions summarized here of the neural systems mediating partisanship and ideological extremism have made it possible to delimit some of the regions and interrelationships, within the cerebral cortex, that seem relevant to sustain entrenched political beliefs and preferences. They disclosed relevant interactions with subcortical and limbic structures that mainly intervene in the affective valence of these attitudes. However, the plausible neural similarities and differences between ordinary partisanship alignments and sectarian and radicalized extremism have not been firmly established, and even less so are the psychobiological ingredients that may lead to crossing the threshold to enter and participate in violent terrorizing actions.

I have proposed paths to progress in this area that can lead to improved predictive adjustment and versatility regarding the psychological ingredients that may promote violent extremism. I have suggested that systematic profiling of individual differences rooted in certain temperamental traits can sophisticate an area of research that is crucial to understand the enactment of agonistic tactics such as terror attacks and the idiosyncratic characteristics of perpetrators involved. Refined and robust characterization of such individual attributes may allow these profiles to be incorporated into the tasks of preventing and counteracting the threatening resurgences of terrorist attacks. Always keeping in mind that political violent extremism usually arises in situations of intergroup conflict [6, 30, 77, 78, 79] and that the interactions and reciprocal influences between leaders and followers that form such kinds of competitive coalitions and combative groups [30, 80, 81], present complex dynamics that require nuanced dissections [82, 83].