Brain scientists generalize from a narrow sample to the species

Akin to the behavioral sciences, brain sciences typically sample from a thin slice of the species. Within the field of psychology, 95% of psychological samples come from countries with only 12% of the world's population (Arnett Reference Arnett2008). Similarly, within the field of human neuroimaging, 90% of peer-reviewed neuroimaging studies come from Western countries (Chiao Reference Chiao2009).

Several factors have contributed to the current WEIRD sampling bias in the brain sciences. First, human neuroscience research programs typically build on either empirical questions inspired by animal models, or case studies of brain damaged patients, or theories from evolutionary psychology. Each of these three starting points for neuroscience research carries implicit assumptions of minimal variability across human populations. Second, researchers have lacked the technology to study culture at the neural level in humans, as human neuroimaging methods have become available only within the past three decades and are still not available in many non-Western regions of the world. The use of neuroimaging is often prohibitively expensive, making it easier for richer, politically stable countries, such as Western industrialized nations, to create the powerful societal infrastructures necessary for novel and timely neuroscientific discovery. The infrastructural advantages afforded to neuroscientists from WEIRD nations create researcher biases in the field that are cyclical and that compound over time as researchers create new experiments and seek empirical evidence consistent with theory and predictions based on prior findings. Hence, our current state of knowledge of mind-brain mappings is largely restricted to scientific observations made from people living within WEIRD nations, leaving a large empirical gap in our understanding of how diverse cultures affect mind, brain, and behavior.

It is not safe for brain scientists to generalize from a narrow sample to the species

In the target article, the authors identify key cultural comparisons that reveal behavioral differences across cultures, including industrialized versus small-scale societies, Western versus non-Western cultures, contemporary American versus non-American Westerners, and contemporary Americans versus other Americans. To the extent that behavior arises from neurobiological processes, it is plausible that this set of cultural comparisons would similarly reveal cultural differences in neural functioning.

Indeed, early efforts by cultural neuroscientists to address the question of how culture influences brain function have proven fruitful, particularly for understanding differences in neurobiological processing between Westerners and East Asians. Westerners engage brain regions associated with object processing to a greater extent relative to East Asians, who are less likely to focus exclusively on objects within a complex visual scene (Gutchess et al. Reference Gutchess, Welsh, Boduroglu and Park2006). Westerners show differences in medial prefrontal activity when thinking about themselves relative to close others, but East Asians do not (Zhu et al. Reference Zhu, Zhang, Fan and Han.2007). Activations in frontal and parietal regions associated with attentional control show greater response when Westerners and East Asians are engaged in culturally preferred judgments (Hedden et al. Reference Hedden, Ketay, Aron, Markus and Gabrieli2008). Even evolutionarily ancient limbic regions, such as the human amygdala, respond preferentially to fearful faces of one's own cultural group (Chiao et al. Reference Chiao, Iidaka, Gordon, Nogawa, Bar, Aminoff, Sadato and Ambady2008, Fig. 1). Taken together, these findings show cultural differences in brain functioning across a wide variety of psychological domains and demonstrate the importance of comparing, rather than generalizing, between Westerners and East Asians at a neural level.

Figure 1. Greater bilateral amygdala response to own-culture relative to other-culture fear faces (from Chiao et al. Reference Chiao, Iidaka, Gordon, Nogawa, Bar, Aminoff, Sadato and Ambady2008).

What about cultural differences in brain function beyond comparisons of Westerners and East Asians? Critically, brain scientists have yet to explore the neurobiological ramifications of cultural contrasts beyond Westerners and East Asians. No research to date has explored comparisons in neural functioning of individuals living in small-scale versus industrialized societies. Additionally, although neuroimaging data do exist for comparing the neural functioning of contemporary Americans with that of other Westerners, such as Europeans, no study to our knowledge has yet explored in a hypothesis-driven manner the possibility that brain–behavior relations may vary as a function of the kind of Western subculture. Social neuroscientists have recently begun to address how childhood socioeconomic status affects brain functioning (Hackman & Farah Reference Hackman and Farah2009); however, the effect of education level (e.g., college vs. no college education) on neural functioning remains unknown. Hence, the current state of knowledge in cultural neuroscience remains woefully behind that of cultural psychology. Yet, the knowledge to date supports the notion that it is not always safe for brain scientists to generalize from a narrow sample to the species and that restricting neuroscientific study to WEIRD populations will not be sufficient for building a comprehensive understanding of human nature.

Behavioral scientists and brain scientists alike will mutually benefit from studying non-WEIRD populations

The journey towards understanding how culture affects human nature is one that behavioral and brain scientists can readily embark on together, and likely with mutual benefits. For instance, where do these cultural differences in brain and behavior come from? One possibility is that psychological and neural diversity comes from differential experience specific to a given culture. Another possibility is that diversity in brain and behavior results from culture-gene coevolution, whereby culture coevolves with genes that regulate endophenotypes, such as brain and behavior. Testing both explanations requires empirical work that examines multiple levels of analysis (e.g., gene, brain, mind, culture) across multiple time scales (e.g., situation, ontogeny, phylogeny).

It is humbling to think of the sheer volume of work that lies ahead to address these timely questions, but by working together, behavioral and brain scientists can offer each other a more complete cultural science than either can construct alone.