Hormones and chemicals
some areas of the brain have the capability to express the receptors of the hormones which influence behavior.(Crews, Sanderson et al. 2010). Hormonally mediated events have crucial roles in central nervous system development and function. Changes in cognitive function therefore, might be correlated with different kinds of hormones.(Schantz and Widholm 2001)
Invertebrates have a hormonal system like vertebrates. There are also hormonal receptors in their nervous system. Each hormone has a specific function and as hormones evolve, behaviors and memory and cognition expand (Lockard, Ebert et al. 2017) (Gruber 2014)
Hormonal, neuropeptide and oxytocin signals are seen in some invertebrates; these hormones are involved in memory and learning. Oxytocin enhances neurotransmission and metabolism. The function of this hormone in invertebrates is similar to its function in the human brain. In Protostomia, for example, there are families that have oxytocin and vasopressin. Both of these hormones are found in modern cephalopods, octopus and cuttlefish. (Minakata 2010) Serotonin is also found in invertebrate drainage to mammals. Genetically dense invertebrates are suitable models for explaining the complexity of serotonin signal pathways. These models explain how serotonin and neuronal structure influence behavior. From these explanations one can conclude how serotonin affects human cognitive function. (Curran and Chalasani 2012)
Oxytocin and its nonmammalian homologues (for example isotocin) have an important role in modulating social behaviors and emotions. Oxytocin in mammals influences social behaviors that do not necessarily benefit the individual(Barraza, McCullough et al. 2011). Mesotocin, a homologue of oxytocin in birds, has a similar role for demonstrating social behavior(Goodson, Schrock et al. 2009). for example many corvids share their food voluntary which is an example for prosocial behavior(De Kort, Emery et al. 2006, von Bayern, de Kort et al. 2007, Scheid, Schmidt et al. 2008, Ostojić, Shaw et al. 2013, Duque and Stevens 2016).(Duque, Leichner et al. 2018)
Fish, in response to emotional stimuli, produce cortisol (Bonga). Some transmitter substances are identified in fish such as dopamine, serotonin and isotocin which are associated with emotional behaviors like reward and mood in humans. (Winberg and Nilsson 1993, Thompson and Walton 2004, Kittilsen 2013)
The role of gonadal hormones in the development of brain areas involved in reproduction has been indicated in many studies (Schantz and Widholm 2001). They play important roles in social behaviors and mating processes.
Recently it has been indicated that early exposure to estrogens and androgens has important functions brain regions not involved in reproduction. One of these is the hippocampus, which plays an important role in learning and memory, particularly spatial learning and memory(McEwen, Gould et al. 2007). Sex differences in spatial learning have been reported. For instance, Male rodents have less mistakes than females on spatial learning and navigating. According to Williams et al. (Williams, Barnett et al. 1990)these differences could be due to differences in the way males and females process spatial information. Steroid hormone also controls some parts of spatial learning and memory ability in mammals (Gouchie and Kimura 1991, Williams and Meck 1991, Roof 1993). In birds, testosterone and estradiol can influence spatial memory (Hodgson, Meddle et al. 2008). Additionally, sex hormones in juvenile birds can affect vocal learning (Bottjer and Johnson 1997). for example among young male swamp sparrows those which are able to copy more syllables, have higher levels of estradiol.(Marler, Peters et al. 1987)
Finally, Thyroid hormone plays an important role in neurobehavioral functions, such as delayed reflex development, and emotionality, and deficits in learning and memory (Davenport 1976, De Kloet, Rosenfeld et al. 1988, Akaike, Kato et al. 1991, Stein, Adams et al. 1991).