via — Growth
“…the subcortex may serve as the source upon which more general representation or knowledge is constructed across the course of development.
Certain numerical abilities appear to be relatively ubiquitous in the animal kingdom, including the ability to recognize and differentiate relative quantities. This skill is present in human adults and children, as well as in nonhuman primates and, perhaps surprisingly, is also demonstrated by lower species such as mosquitofish and spiders, despite the absence of cortical computation available to primates. This ubiquity of numerical competence suggests that representations that connect to numerical tasks are likely subserved by evolutionarily conserved regions of the nervous system.
These findings suggest conservation of ontogenetically and phylogenetically lower-order systems in adults’ numerical abilities. The involvement of subcortical structures in representing numerical quantities provokes a reconsideration of current theories of the neural basis of numerical cognition, inasmuch as it bolsters the cross species continuity of the biological system for numerical abilities.
Despite major neuroanatomical differences, adults, infants, nonhuman primates, and invertebrates possess the ability to evaluate relative quantities. Humans’ ability starts with coarse granularity (distinguishing ratios of numerical quantities of 3:1 or larger), but this becomes increasingly precise over development. This series of experiments demonstrates a role of the subcortex in discriminating numerosities in larger (4:1 or 3:1), but not in smaller ratios…this study implicates the human subcortex as a possible source of core number knowledge that is both related to phylogenetic numerical competence and serves as the foundation on which more complex ontogenetic numerical skills may be built.
…different species of fish also appear to have coarse number representations. Mosquitofish can perform various numerical tasks including picking larger shoals, choosing more companions or mates, or discriminating larger quantities, and guppies have been shown to differentiate ratios with levels of precision similar to that of undergraduate college students.
he ability to process number may be relatively ubiquitous in the animal world…these numerical feats are accomplished by animals without well-developed cerebral cortices, and the [areas], heavily implicated in human and nonhuman primate numerical cognition, is entirely absent in some of these species. Number processing in these species, therefore, likely relies on older, more evolutionarily conserved regions of the nervous system…computational models provide evidence that visual number judgments are possible even with relatively small networks.
One candidate region that might serve the phylogenetic bridge is human subcortex, a region largely neglected in contemporary research of numerical cognition. The involvement of subcortical structures in coarse numerical representation provokes a reconsideration of current theories of number perception, which are reliant on cortical-level processing, inasmuch as it bolsters the cross species continuity of the biological system for numerical knowledge.
…the presence of a coarse subcortical number processor that makes contributions to numerical processing, independently of cortex, thereby serving as the link between lower- and higher-order species. Specifically, we expect the subcortical mechanism to respond selectively to nonsymbolic quantities given that symbolic manipulation of quantities is uniquely human and likely requires cortical contributions. Moreover, we predict that subcortical contributions to number processing will be ratio dependent…
…we exploit a psychophysical method that allows us to differentiate between cortical vs. subcortical, monocular visual signals before layer IV of primary visual cortex. Before this layer, the monocular signals of the visual system are propagated by separate sets of neurons, but beyond layer IV, signals from each eye are no longer segregated, and, because there are relatively few monocular neurons beyond area V1, activation of extrastriate areas is not eye dependent.
The findings from this study uncover the contribution of a subcortical number system in human adults. The extent to which this system participates in any of the other (multiple) forms of numerical computation (such as arithmetic) and the relationship between the observed subcortical facilitation and cortical processes remain to be determined. However, several possible alternatives exist. One possibility is that the monocular advantage and its subcortical neural correlate might act independently of cortex, perhaps as an evolutionary vestige, that plays no real functional role in more complex number processing. A second possibility is that, at least in human adults, such computations serve a functional role and signals from these prestriate regions are then propagated for later cortical processing.
The presence of such coarse number processing in children suggests that more complex numerical abilities are likely not innate (29) and are certainly not adult-like, and, thus, a more basic approximate system such as the one we propose might serve as the basis of the rudimentary skills exhibited by the infants. In line with this idea, a recent developmental electroencephalography study reports little evidence for cortical involvement of numerosity processing in very young children and rather that the cortical mechanism for numerosity perception develops gradually throughout childhood. Thus, the numerosity competence of the subcortical mechanism might serve to bootstrap cortical mechanisms early in development.
The numerosity evaluation ability documented here may be…a rudimentary, evolutionarily conserved system that computes coarse properties of the input may suffice and may be mediated by subcortical systems. The coarse signals computed by these lower-order structures are then propagated to cortex and serve as the training signal for more precise cortical…processes, likely resulting in the well-established contribution of parietal cortex to mathematical skills. The ratio-dependent sensitivity to numerosity of the subcortical system, although key during development, may still be uncovered in adults and may contribute functionally.
In conclusion, the current set of experiments shows that, in the context of a stereoscopic setting, the adult human subcortex computes quantity, which results in facilitated numerical judgments. This facilitation exhibits ratio dependence and generalizes to both small and large quantities. The numerical representations in the subcortex uncovered here may relate to the ontogenetic developmental knowledge of number and the ubiquitous number knowledge across phylogeny.
“Numerosity representation is encoded in human subcortex” Elliot Collinsa,”