. Despite the broad variability in brain size across species, there is little variation in the thickness [605596]

. Despite the broad variability in brain size across species, there is little variation in the thickness
of the cerebral cortices that varies relatively little between brains of different sizes. The variation
observed within a given brain is similar to that found between species of different brain size
(DeFelipe, 2011). In a valiant effort, Javier DeFelipe compared the thickness of lamination (see
Fig. 3) of frontal, parietal, and occipital cortices across nine species, including the mouse, rat,
rabbit, goat, cat, cheetah, lion, dog, and human. As pointed out by DeFelipe (2011), the thickest
part of the cerebral cortex is in the human motor cortex , which can reach up to 4.5 mm, in striking
contrast with the depths of the fissures that may only be 1 mm t hick. Also, there are marked
differences across brain areas where, for example, the thickness of dog’s frontal cortex is 0.8 mm,
while the thickness in parietal cortex is 1.6 mm. Regardless of the several thousand times
difference between the brain size of whales and that of pygmy shrew, there seems to be no
difference in the lamination of cerebral cortex in the pygmy shrew (0.4 mm thickness), and in
whales (less than 2 mm thick). Furthermore, the appearance of the cellular components in Nissl –
stained sec tions is generally similar in all cortices. Another observation stemming from the
lamination thickness of frontal cortex is that the supra -granular layers in humans are the thickest
across all species shown in Fig. 3. Altogether, these observations suggest that the increased brain
size may be regarded as the main developmental drive across species.

2.3 Animal brain connectome . A connectome is a structural map of the “wiring diagram” of
neural connections in the animal brain. More broadly, an animal connec tome would include the
mapping of all neural connections within an animal's nervous system. The visualization of the
detailed anatomic structures of the mouse brain is obtained from a diffusion MRI tractography of
the mouse brain and comparison with neuron al tracer data in Fig. 4.

3.1. Rationale . Looking from a historic perspective to understand animal cognition, Descartes
argued that all animals behave like “machines” (i.e. “simple reflex devices”) that do not think
because they lack language ability (Ram baugh et al., 1996). From another perspective, Charles
Darwin came with a totally different view on animal behavior, by defending their ability to think,
even in the absence of language (Thierry, 2010). Contrary to Descartes’s view, today it is well
docu mented, that “animals use their thinking ability to represent events and objects in their
environments (Grieves and Jeffery, 2017). Surprising insights into the animals mind and their
communication abilities provide “ample evidence that animals do think” (Larkin, 2013). If animals
think, the next question to ask is: what does this imply about their brains? "If an animal turns out
to think in a similar way as we do, did the animal develop a brain similar to humans? Or is the
animal able to come up with the s ame kind of thought but with a completely different brain?"
(Prior et al, 2008).
3.2. Animals cognitive functions. The spectrum of animal cognitive functions is quite broad.
Here, are shown some examples of such functions with the neural correlates of ani mal’s mind.
3.2.1. Human face recognition in dog. Dogs have a complex social relationship with humans.
One fundamental clue in support of this claim is the manner in which dogs pay close attention to
human faces in order to guide their behavior. For exam ple, they recognize their owner’s emotional
state using visual cues (Cuaya et al., 2015). To understand how dogs’ brains perceive human faces,
Cuaya and his colleagues trained seven dogs to remain awake, still, and unrestrained inside an
MRI scanner (Fig. 5), while their brain was scanned using functional magnetic resonance imaging
(fMRI).

A visual stimulation paradigm was used to compare animal’s brain activity elicited by human faces
versus everyday objects. Cuaya’s experimental results are showing s ignificant brain activation

related to the perception of faces, mainly in the bilateral temporal cortex, with no significant brain
activity change to everyday objects. Cuaya’s results are consistent with reports in humans and
other animals like primates an d sheep that suggest a high degree of conservation of ventral visual
pathway for face processing. This study confirms the role of the temporal cortex as node in
circuitry of social cognition in dogs (Cuaya et al., 2015).
3.2.2. Elephant’s memory. A question like: Do elephants never forget? may be an exaggeration,
but nevertheless, the elephants rank among the smartest animals on the planet. Elephants have the
largest brains of all terrestrial mammals, weighing around 5 kg (see figure 6) for an adu lt animal
(Conger, 2017; Soshani et al., 2006). Although the brain size alone cannot tell us how effectively
the brain works, nevertheless, it can provide a salient hint about the power of elephant’s memory.
As shown in part 2, an animal's intelligence is evaluated by the encephalization quotient (EQ).
Thus, the higher the ratio of brain -to-body -mass, the smarter the animal is and vice versa. For
example, humans have an average EQ above 7, elephants of 1.88 and pigs around 0.27 (Shoshani
et al., 2006). Fema le elephants, as the leaders of matriarchal elephant herds, show signs of better
memory, alerting their herd if a potential danger arises or if a feeding ground is recognized

An elephant's memory encodes information necessary for survival, such as f oraging locations and
family members identification, in the same manner that human working memory systems
selectively discard or transfer data for long -term memory storage (or future retrieval) ( Harta et al.,
2008 ). There is clear evidence that elephants have an excellent ability to remember relevant spatial
details about their environment for a very long time.

3.2.3. Executive decision making in sheep and goat. The sheep . Compared to macaque monkeys,
the sheep seems to have a similar brain size, but not the same level of intelligence, and therefore,
sheep is not used for testing in pre -clinical cognitive studies (Morton and Avanzo, 2011).