Suzana Herculano-Houzel

Cytoarchitectural characteristics associated with cognitive flexibility in raccoons

(2021), Joanna Jacob; Molly Kent; Sarah Benson-Amram; Suzana Herculano-Houzel; Mary Ann Raghnati; Emily Ploppert; Jack Drake; Bilal Hindi; Nick R. Natale; Sarah Daniels; Rachel Fanelli; Anderson Miller; Tim Landis; Amy Gilbert; Shylo Johnson; Annie Lai; Molly Hyer; Amanda Rzucidio; Chris Anchor; Stan Gehrt; Kelly Lambert, The Journal of Comparative Neurology

Energy supply per neuron is constrained by capillary density in the mouse brain

(2022), Lissa Ventura-Antunes; Suzana Herculano-Houzel, Frontiers in Integrative Neuroscience

Neuronal densities vary enormously across sites within a brain. Does the
density of the capillary bed vary accompanying the presumably larger energy
requirement of sites with more neurons, or with larger neurons, or is energy
supply constrained by a mostly homogeneous capillary bed? Here we find
evidence for the latter, with a capillary bed that represents typically between
0.7 and 1.5% of the volume of the parenchyma across various sites in the
mouse brain, whereas neuronal densities vary by at least 100-fold. As a result,
the ratio of capillary cells per neuron decreases uniformly with increasing
neuronal density and therefore with smaller average neuronal size across sites.
Thus, given the relatively constant capillary density compared to neuronal
density in the brain, blood and energy availability per neuron is presumably
dependent on how many neurons compete for the limited supply provided by
a mostly homogeneous capillary bed. Additionally, we find that local capillary
density is not correlated with local synapse densities, although there is a small
but significant correlation between lower neuronal density (and therefore
larger neuronal size) and more synapses per neuron within the restricted
range of 6,500–9,500 across cortical sites. Further, local variations in the
glial/neuron ratio are not correlated with local variations in the number of
synapses per neuron or local synaptic densities. These findings suggest that
it is not that larger neurons, neurons with more synapses, or even sites with
more synapses demand more energy, but simply that larger neurons (in low
density sites) have more energy available per cell and for the totality of its
synapses than smaller neurons (in high density sites) due to competition for
limited resources supplied by a capillary bed of fairly homogeneous density
throughout the brain.

High associative neuron numbers could drive cognitive performance in corvid species

(2022), Felix Stöckens; Kleber Neves; Sina Kirchem; Christine Schwab; Suzana Herculano-Houzel; Onur Güntürkün, The Journal of Neuroscience

Abstract:> Corvids possess cognitive skills matching those of nonhuman primates. However how these species with their small brains achieve such feats remains elusive. Recent studies suggest that cognitive capabilities could be based on the total numbers of telencephalic neurons. Here we extend this hypothesis further and posit that especially high neuron counts in associative pallial areas drive flexible complex cognition. If true avian species like corvids should specifically accumulate neurons in the avian associative areas meso- and nidopallium. To test the hypothesis we analyzed the neuronal composition of telencephalic areas in corvids and noncorvids (chicken pigeons and ostriches—the species with the largest bird brain). The overall number of pallial neurons in corvids was much higher than in chicken and pigeons and comparable to those of ostriches. However neuron numbers in the associative mesopallium and nidopallium were twice as high in corvids and in correlation with these associative areas the corvid subpallium also contained high neuron numbers. These findings support our hypothesis that large absolute numbers of associative pallial neurons contribute to cognitive flexibility and complexity and are key to explain why crows are smart. Since meso-/nidopallial and subpallial areas scale jointly, it is conceivable that associative pallio-striatal loops play a similar role in executive decision making as described in primates.