Introduction The problem of function localization in the brain is one of the most fundamental in neuroscience. There are two opposite paradigms relating to the problem: “modularism,” also known as “localism,” versus “holism,” which have been discussed for a long time ( 1 , 2 ). The debate in favor of one or another view can still be traced at all methodological levels – from the cell to the system. In this opinion paper we want to raise a question – what is meant nowadays by brain mapping? In addition, we want to highlight the necessity of being aware of occasionally occurring discontinuity in the research at different methodological scales. This problem is evident for experts in the field, but not always sufficiently so for early career researches. We will try to describe the difficulties of modern brain mapping primarily by looking at one of the currently best-studied functions – motor function. History of Opposition of Modular Versus Holistic Conceptions of Brain Organization A somewhat artificial opposition of “modular” and “holistic” organization of the brain has been evident in neuroscience from 18th century, and started mostly as a disagreement between physiologists working on animals and clinicians studying brain lesions in humans ( 1 – 3 ). A first revision of the term “function” by a clinician and a step away from hardwired localism was performed by the neurologists J. H. Jackson at the end of 19th century who wrote that “localization of a symptom is not localization of a function” ( 4 ). In the beginning of the 20th century, a paradigm shift occurred toward gestalt psychology, which changed the trend of research at the macro-scale level towards a more holistic view ( 2 ). A prime example of a confrontation at the micro-scale at the same time was the debate of Golgi and Cajal regarding the essence of a neuron ( 5 ). In 1937, a neurosurgeon W. Penfield performed the first cortical cartography in humans and published an iconic description of sensory and motor homunculi ( 6 ). In the second quarter of the 20th century, the concept of a function as a goal-dependent entity appeared in the form of theory of movements ( 7 ) and theory of functional systems ( 8 ), both viewing a function as a non-rigid goal-dependent entity. To date, it is usually postulated that localism and holism have been replaced by “connectionism,” with many studies nowadays trying to find interactions between brain regions and not the function of these regions by themselves ( 9 , 10 ). However, it seems there is still a tendency to favor localism, especially in the cognitive sciences ( 11 , 12 ). Perhaps, this is due to the fact that modern non-invasive methods, such as PET, fMRI or TMS, are mostly associated with functional mapping of the brain based on M. Minsky’s philosophy that “minds are what brains do.” Discontinuity of the Motor Research of Different Methodological Scales The question remains open of how cortical “activation” at the macro-level, viewed for example with fMRI or EEG, is linked to micro-scale phenomena such as single neuron activity in the spinal cord in awake animals (especially in humans) ( 13 , 14 ). There is a large community of researches studying ways of activation of a particular alpha-motor neurons in the spinal cord ( 15 – 17 ); scientists working on the level of a single neuron usually associate it to a specific task ( 16 , 18 ). Thereby, those who work with slices of the spinal cord are well aware of how to activate a certain motoneuron ( 19 ), but it is still difficult to bridge these phenomena with activation of the cortex ( 15 ). Modern macro-scale approaches connecting peripheral and central recording, such as TMS-EEG and corticomuscular coherence, including biofeedback, are trying to overcome this gap ( 20 ). A good example of a discontinuity in motor research at different methodological scales is the phenomena of convergence and divergence of motor cortex organization. They are well known in micro- and meso-scale studies. For example, in the invasive brain–computer interface (BCI) research, principles like neural degeneracy and neuronal multitasking were formulated ( 21 ). However, these phenomena are still widely overlooked in the research at the macro-scale level ( 22 ). For instance, a commonly used term in macro-scale research is an “area of a muscle cortical representation” ( 23 , 24 ), which is suitable for practical use like presurgical motor mapping ( 25 ), but is physiologically dubious considering the proven fact that some pyramidal cells may broadly innervate corresponding alpha motoneurons relating to activation of different muscles, even of different limb segments ( 26 – 28 ). Goal-Driven Concept of a Function – Problem of Awake Versus Anesthetized Animals Clearly demonstrated in many studies, context and goal-dependency of a motor function ( 29 , 30 ) brings us back to the necessity to revise the concept of a function as an environment and goal-dependent entity. Since a large amo
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