Written By: Diyanka Lahane
Introduction
While growing up, children are taught that animals can be anything ranging from the smallest ant to the largest elephant. However, for most of our education, we focus heavily only on the anatomy of mammals, specifically humans. Whilst human anatomy and health is an incredibly important educational topic for youth, this focus causes a disconnect in how we perceive other animal groups. Are other animals really that different from humans? In fact, how different are other mammals to humans to lizards to pigeons and so on?
Animals are separated into vertebrates and invertebrates. Invertebrates are animals that do not have a spine/backbone. This can include insects such as butterflies and wasps. Vertebrates are a separate classification of animals; they do have a spine/backbone and a hard-shell skull to protect the brain. This includes birds, reptiles, mammals, and amphibians. In this article, we will discuss anatomical differences and similarities in the brain and its function amongst three specific groups: mammals, birds, and reptiles. Do these anatomical similarities lead to common cognitive abilities amongst the groups or are their differences too great?
It is important to be well informed in this topic as understanding anatomical differences can explain cognitive advantages and disadvantages between animal groups. It will provide a basis for further research in ecological roles for various species, insight to evolutionary patterns across groups, and policy for animal conservation organizations.
Birds
Bird brains, also known as avian brains, function very similarly to mammalian brains despite having different neuroanatomy. Specifically, “connectional similarities in the brains” of both animal groups allow for conclusions to be drawn that both groups have similar cognitive function (Emery, N.J., Clayton, N.S., 2005). A mammalian brain’s neocortex consists of six layers, each layer having its own chemical composition and neural pathways (Emery, N.J., Clayton, N.S., 2005). The neocortex is important in regards to planning and critical thinking. Unlike mammalian braids, avian brains do not have any laminar organization aside from the dorsal surface on the forebrain which is three layers. Additionally, although avian brains do have their own neocortex, it does not have the same function as a mammal’s neocortex. Rather, bird brains have a large pallium- upper layer of the avian forebrain- that controls memory, learning, problem-solving, and so on (Jarvis, E.D., Güntürkün, O., Bruce, L., et al. 2005). Any brain lesions in this part of the avian brain could lead to problems in working memory or delayed reversal learning (Emery, N.J., Clayton, N.S., 2005). While the specific anatomical part of the avian brain is recognized, there has not been enough research to further differentiate it from the mammalian brain or find further function (Jarvis, E.D., Güntürkün, O., Bruce, L., et al. 2005).
Additional research found that avian brains have a similar visual, somatosensory, and auditory (sight, touch, and hearing) pathways to the mammalian brain. Both pathways receive input from the thalamus and this information is processed in the neocortex for mammals and neostriatum and hyperstriatum in birds. The neostriatum and hyperstriatum are parts of the pallium. Avian brains have a different anatomical make-up of the mammal’s prefrontal cortex (Jarvis, E.D., Güntürkün, O., Bruce, L., et al. 2005).
The pallium in avian brains is more similar to reptiles than mammals. Palladium is the grey and white matter that covers the cerebrum. There are four sections of the pallium: medial, dorsal, lateral, and ventral. The medial section of pallium is the hippocampus for both mammals and birds and medial cortex for reptiles. The neocortex in mammals is the dorsal ventricular ridge (DVR) which is just the lateral and ventral pallium in birds and reptiles (Rattenborg, N.C., Martinez-Gonzalez, D., 2011). Neurogenesis is the process of creating new neurons in the brain. While little research has been done on this topic, a trend in birds is that neurogenesis changes seasonally in the hippocampus and the part of the brain that controls song control. Neuron production is at its peak in the breeding season (Garcia-Verdugo, J.M., Ferrón, S., Flames, N., et al, 2002). In mammals, neuron development occurs before the mammal becomes an adult whereas the opposite is true for birds.
Reptiles
Birds and mammals are the two groups where the hippocampus is crucial for cognition and memory. Do reptiles fall under that category as well, or do they have a different neural mechanism? Mammals, such as humans, need the hippocampus to form long-term memories. Certain brain lesions can hinder the hippocampus from connecting to other parts of the brain, which stop the formation of more episodic memories (Rattenborg, N.C., Martinez-Gonzalez, D., 2011). Information passes through primary and secondary cortices before entering the hippocampus. However, the hippocampus does not just receive several bits of sensory information, but instead a heavily processed multi-level piece of information that results in a memory. Similar to birds and mammals, reptiles have a spatial learning ability, however they are not hippocampus-dependent. Instead, most of their memory learning is through the medial cortex (Rodriguez, F., López, J.C., Vargas, J.P., et al, 2002).
Reptiles and mammals have similar cortex structure. However, instead of the six-layered structure like a mammal, reptiles have a clear three-layer structure. While there is lacking evidence regarding specificity of motor and somatosensory pathways, it is concluded that reptiles have a simpler and significantly less complex cognitive ability. This means that reptiles do not have several different forms of information processing, unlike mammals which have several different processing pathways (Naumann, R.K., Ondracek, J.M., Reiter, S., et al, 2015).
There is not much research on reptiles entirely, due to difficulty maintaining a large sample size with a fast life cycle. However in a recent study, lizards were tested in their spatial cognition ability to determine how their evolved learning strategy is. This experiment was done to question the belief that reptiles have instinct-driven learning. When lizards are placed in a new environment, it is concluded that mapping strategies were used to determine the lizard’s location. This means that lizards, and most reptiles, can recognize visual placeholders as a frame of reference for necessities like shelter or bodies of water (Font, E., 2019).
Conclusion
In conclusion, each animal group has unique neuroanatomical formation that is dependent on their lifestyle and ecological adaptations. Throughout one’s education, it is constantly reinforced that mammals have the most complex cognition ability across all animal groups. Although the anatomical structures of mammals are most complex, other animal groups can still perform higher processing functions with less complex neuroanatomical structures. Further research should be conducted on the evolutionary basis of birds and reptiles and how their environment can affect higher cognition.
Resources
Emery, N.J., Clayton, N.S. (2005). Evolution of the avian brain and intelligence. Current Biology, 15(23). https://doi.org/10.1016/j.cub.2005.11.029
Font, E. (2019). Rapid learning of a spatial memory task in a lacertid lizard (Podarcis liolepis). Behavioral Processes, 169. https://doi.org/10.1016/j.beproc.2019.103963
Garcia-Verdugo, J.M., Ferrón, S., Flames, N., Collado, L., Desfilis, E., Font, E. (2002) The proliferative ventricular zone in adult vertebrates: a comparative study using reptiles, birds, and mammals. Brain Research Bulletin, 57(6); 765-775. https://doi.org/10.1016/S0361-9230(01)00769-9
Jarvis, E.D., Güntürkün, O., Bruce, L., Csillag, A., Karten, H., Kuenzel, W., et al. (2005). Avian brains and a new understanding of vertebrate brain evolution. National Reviews Neuroscience, (6);151-159. https://doi.org/10.1038/nrn1606
Naumann, R.K., Ondracek, J.M., Reiter, S., Shein-Idelson, M., Tosches, M.A., Yamawaki, T.M., et al. (2015). The reptilian brain. Current Biology, 25(8); 317-321. https://doi.org/10.1016/j.cub.2015.02.049
Rattenborg, N.C., Martinez-Gonzalez, D. (2011). A bird-brain view of episodic memory. Behavioral Brain Research, 222(1); 236-245. https://doi.org/10.1016/j.bbr.2011.03.030
Rodriguez, F., López, J.C., Vargas, J.P., Broglio, C., Góomez, Y., Salas, C. (2002). Spatial memory and hippocampal pallium through vertebrate evolution: insights from reptiles and teleost fish. Brain Research Bulletin, 57(3-4); 499-503. https://doi.org/10.1016/S0361-9230(01)00682-7
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