We are interested in why our brain is organized the way it is. Specifically, we are interested in how differences in brain organization, for instance between different primate species' brains or between different individuals, are related to differences in behavioral repertoires. To date, we have mostly focused on one particular aspect of brain organization--connectivity. We try to understand how areas of the brain are connected, why they are connected in that way, and how their interactions are related to behaviour. We employ a wide range of experimental techniques to try to understand these processes.

Roughly, our research concentrates around three themes that represent the who, how, and why of brain organization:

Who? Or: Which brain regions can we find and what is the architecture of connections between them?

How? Or: How does the brain work and how does activity in one brain region influence activity in another?

Why? Or: Why is the brain organized the way it is?


Who?

This part of our research is aimed at mapping areas of the brain in humans and non-human primates and to investigate the connections between these areas. The connections of brain regions constrain their inputs and output and thus give us vital clues about their function. We use diffusion-weighted imaging and resting state functional MRI to study the architecture of connections between brain areas and have developed a number of ways to compare these architectures between species.

Relevant publications:

Schurz M, Tholen MG, Perner J, Mars RB, & Sallet J (2017) Specifying the brain anatomy underlying temporo-parietal junction activations for theory of mind: A review using probabilistic atlases from different imaging modalities. Human Brain Mapping 38:4788-4805
Mars RB, Foxley S, Jbabdi S, Sallet J, Noonan MP, Andersson JL, Verhagen L, Croxson PL, Dunbar RIM, Khrapitchev AA, Sibson N, Miller KL, & Rushworth MFS (2016) The extreme capsule fiber complex in humans and macaques: A comparative diffusion MRI tractography study. Brain Structure and Function 221:4059-4071
Neubert FX, Mars RB, Sallet J, & Rushworth MFS (2015) Connectivity reveals relationship of brain areas for reward-guided learning and decision making in human and monkey frontal cortex. Proceedings of the National Academy of Sciences USA 112:E2695-E2704
Neubert FX, Mars RB, Thomas AG, Sallet J, & Rushworth MFS (2014) Comparison of human ventral frontal cortex areas for cognitive control and language with areas in monkey frontal cortex. Neuron 81:700-713
Sallet J, Mars RB, Noonan MP, Neubert FX, Jbabdi S, O'Reilly JX, Filippini N, Thomas A, & Rushworth MFS (2013) The organization of dorsal prefrontal cortex in humans and macaques. Journal of Neuroscience 33:12255-12274
Mars RB, Sallet J, Neubert FX, & Rushworth MFS (2013) Connectivity profiles reveal the relationship between brain areas for social cognition in human and monkey temporoparietal cortex. Proceedings of the National Academy of Sciences USA 110:10806-10811
Mars RB, Sallet J, Schüffelgen U, Jbabdi S, Toni I, & Rushworth MFS (2012) Connectivity-based subdivisions of the human right 'temporoparietal junction area' (TPJ): Evidence for different areas participating in different cortical networks Cerebral Cortex 22:1894-1903
Mars RB, Jbabdi S, Sallet J, O'Reilly JX, Croxson PL, Olivier E, Noonan MP, Bergmann C, Mitchell AS, Baxter MG, Behrens TEJ, Johansen-Berg H, Tomassini V, Miller KL, & Rushworth MFS (2011) Diffusion-weighted imaging tractography-based parcellation of the human parietal cortex and comparison with human and macaque resting state functional connectivity. Journal of Neuroscience 31:4087-4100
Rushworth MFS, Boorman E, & Mars RB (2009) Comparing brain connections in different species using diffusion weighted imaging. In: Johansen-Berg H & Behrens TEJ (Eds.) Diffusion MRI: From quantitative measurement to in vivo neuroanatomy, pp. 445-460. Amsterdam: Academic Press


How?

How does brain architecture relate to brain function? We use a variety of neuroimaging methods to study how the human brain works and how this relates to the connections between regions. Using functional neuroimaging we investigate brain activation during task performance and how this is dependent on the interactions between brain areas. Using brain stimulation methods we causally interfere with activity in specific brain regions and investigate how this influences activity in the rest of the brain and, in turn, how this influence relies on the white matter connections between brain areas.

Relevant publications on the relation between brain architecture and brain function:

Zimmermann M, Mars RB, De Lange FP, Toni I, & Verhagen L (2018) Is the extrastriate body area part of the dorsal visuomotor stream? Brain Structure and Function 223:31-46
Smith AT, Beer AL, Furlan M, & Mars RB (2018) Connectivity of the cingulate sulcus visual area (CSv) in the human cerebral cortex Cerebral Cortex 28:713-725
Tavor I, Parker Jones O, Mars RB, Smith SM, Behrens TE, & Jbabdi S (2016) Task-free MRI predicts individual differences in brain activity during task performance. Science 352:216-220
O'Reilly JX, Croxson PL, Jbabdi S, Sallet J, Noonan MP, Mars RB, Browning PG, Wilson CR, Mitchell AS, Miller KL, Rushworth MFS, & Baxter MG (2013) A causal effect of disconnection lesions on interhemispheric functional connectivity in rhesus monkeys. Proceedings of the National Academy of Sciences USA 110:13982-13987
Mars RB, Piekema C, Coles MGH, Hulstijn W, & Toni I (2007) On the programming and reprogramming of actions. Cerebral Cortex 17:2972-2979

Relevant publications using brain stimulation to probe or influence neural interactions:

Johnen V, Neubert FX, Buch ER, Verhagen L, O'Reilly J, Mars RB, & Rushworth MFS (2015) Causal manipulation of functional connectivity in a specific neural pathway during behaviour and at rest. eLife 4:e04585
Van Campen AD, Neubert FX, Van den Wildenberg WPM, Ridderinkhof KR, & Mars RB (2013) Paired-pulse transcranial magnetic stimulation reveals probability-dependent changes in functional connectivity between right inferior frontal cortex and primary motor cortex during go/no-go performance. Frontiers in Human Neuroscience 7:736
Mars RB, Neubert FX, & Rushworth MFS (2011) Top-down control over the motor cortex. In: Mars RB et al. (Eds.) Neural basis of motivational and cognitive control, pp. 111-125. Cambridge: MIT Press
Neubert FX, Mars RB, Buch ER, Olivier E, & Rushworth MFS (2010) Cortical and subcortical interactions during action reprogramming and their related white matter pathways. Proceedings of the National Academy of Sciences USA 107:13240-13245
Mars RB, Klein MC, Neubert FX, Olivier E, Buch ER, Boorman ED, & Rushworth MFS (2009) Short-latency influence of medial frontal cortex on primary motor cortex during action selection under conflict. Journal of Neuroscience 29:6926-6931


Why?

Our brain differs dramatically from that of other primates. It is larger overall, some areas have expanded disproportionally, and the connections between areas have changed. These differences are paralleled by differences in our behavioral repertoire. The ultimate goal of our research is to understand how differences in brain organization are related to differences in behaviour and how this has been driven by the evolutionary challenges that different lineages in the animal kingdom have faced. To date, this research has focused mostly on how primates' social abilities and foraging niche are related to their brain organization. Moreover, we look at how individual differences between people's behavior in these domains relate to differences in their brain organization. We have also written some more general overviews of what makes brains different and how to tackle this question.

What makes brains different?

Mars RB, Eichert N, Jbabdi S, Verhagen L, & Rushworth MFS (2018) Connectivity and the search for specializations in the language-capable brain. Current Opinion in Behavioral Sciences 21:19-26
Mars RB, Passingham RE, Neubert FX, Verhagen L, & Sallet J (2017) Evolutionary specializations of human association cortex. In: Kaas JH (Ed.) Evolution of Nervous Systems (2nd edition, vol. 4), pp. 185-205. Oxford: Elsevier
Mars RB, Neubert FX, Verhagen L, Sallet J, Miller KL, Dunbar RIM, & Barton RA (2014) Primate comparative neuroscience using magnetic resonance imaging: Promises and challenges. Frontiers in Neuroscience 8:298

Relevant publications on the relationship between brain organization and social abilities:

Noonan MP, Sallet J, Mars RB, Neubert FX, O'Reilly JX, Andersson JL, Mitchell AS, Bell AH, & Rushworth MFS (2014) A neural circuit covarying with social hierarchy in macaque. PLoS Biology 12:e1001940
Brazil IA, Hunt LT, Bulten BH, Kessels RPC, De Bruijn ERA, & Mars RB (2013) Psychopathy-related traits and the use of reward and social information: A computational approach. Frontiers in Psychology 4:952
Rushworth MFS, Mars RB, & Sallet J (2013) Are there specialized circuits for social cognition and are they unique to humans? Current Opinion in Neurobiology 23:436-442
Mars RB, Neubert FX, Noonan MP, Sallet J, Toni I, & Rushworth MFS (2012) On the relationship between the 'default mode network' and the 'social brain'. Frontiers in Human Neuroscience 6:189
Sallet J, Mars RB, Noonan MP, Andersson J, O'Reilly JX, Jbabdi S, Croxson PL, Miller KL, Jenkinson M, & Rushworth MFS (2011) Social network size affects neural circuits in macaques. Science 334:697-700

Relevant publications on the relationship between brain organization and foraging:

Kolling N, Wittmann MK, Behrens TEJ, Boorman ED, Mars RB, & Rushworth MFS (2016) Value, search, persistence and model updating in anterior cingulate cortex. Nature Neuroscience 10:1280-1285
Rushworth MFS, Kolling N, Sallet J, & Mars RB (2012) Valuation and decision-making in frontal cortex: One or many serial or parallel systems? Current Opinion in Neurobiology 22:946-955
Kolling N, Behrens TEJ, Mars RB, & Rushworth MFS (2012) Neural mechanisms of foraging. Science 336:95-98