Amygdala
Amygdala is a part of telencephalon and plays the most important role in
emotional learning, reward, motivation (Cardinal, Parkinson et al. 2002,
Berridge and Robinson 2003, Balleine 2005).(Laberge, Mühlenbrock-Lenter
et al. 2006)
Due to its association with the regions involved in cognition
(especially the neocortex and the hippocampus), the amygdala can affect
cognition.The amygdala is also an important system in emotional
computing.(LeDoux 1989)
The functional systems of the amygdala possess sensory input from early
stations of the chemical senses (olfaction and taste), visceral sensory
afferents and higher-order thalamic and cortical input from all sensory
modalities, in addition to an output to autonomic and visceral centers
in the brainstem and connections to the limbic cortex.(Laberge,
Mühlenbrock-Lenter et al. 2006)
Neurobehavioral studies imply that, medial pallium of fishes probably
have similar functions in emotional learning as well as amygdala; they
are homologous structures. (Durán, Ocaña et al. 2010, Demski 2013,
Duvarci and Pare 2014, Janak and Tye 2015, Uceda, Ocaña et al. 2015).
The teleost amygdala is thought to reside in the medial region of the
dorsal pallium (Dm) (Rink and Wullimann 2002, Northcutt 2006, Jesuthasan
2012)
Functional studies about the amphibian amygdala are rare; however,
according to Swanson and Petrovich(Swanson and Petrovich 1998), the
limbic associative component of the amphibian amygdaloid complex is not
homologous to the frontotemporal cortical component of mammals since
they have different developmental origins. Moreover it is indicated that
amphibians do not possess a basolateral amygdaloid complex involved in
the motivational effects of emotion(Cardinal, Parkinson et al. 2002).
This implies that anamniotes have a limited repertoire of learning
responses compared to amniotes.(Laberge, Mühlenbrock-Lenter et al. 2006)
The absence of aversive emotions (such as fever or increased heart
rate)(Cabanac 1999, Paradis and Cabanac 2004) and taste aversion in fish
and amphibians (Paradis and Cabanac 2004)due to the absence of
basolateral amygdaloid complex, and also the participation of amygdala
in emotional learning in mammals ,suggests that the advent of the
basolateral amygdaloid complex and its reptilian equivalent have brought
genuine innovations to vertebrates’ emotional behavior. (Laberge,
Mühlenbrock-Lenter et al. 2006)
According Lanuza et al. (Lanuza, Belekhova et al. 1998)PDVR, the
dorsolateral and the lateral amygdala are functionally similar to the
mammalian basolateral complex. Thus, ADVR of reptiles is not part of the
amygdala. However an alternative interpretation represents that the ADVR
is homologous to the mammalian lateral nucleus of the amygdala. (Bruce
and Neary 1995, Fernandez, Pieau et al. 1998). It is also suggested
that, the PDVR of reptiles is involved in emotional behavior.(Tarr 1977,
Distel 1978, Sugerman and Demski 1978, Laberge, Mühlenbrock-Lenter et
al. 2006)
Amygdala in birds includes two regions: subpallial amygdaloid nuclei
that is the nucleus taeniae of the amygdala (TnA) and the newly
identified subpallial amygdala (SpA).(Yamamoto, Sun et al. 2005). In
birds archistriatal structure, includes the posterior and medial
archistriatum outlined Nucleus taenia (Tn) which is a discrete
component. Based on hypothalamic formation, the posterior and medial
archistriatum is homolog of amygdala in mammals.(Cheng, Chaiken et al.
1999) The part of amygdala in mammals which originated from ventral
pallium is called pallial amygdala. Tn can demonstrate many of the
structural and functional features of the amygdaloid complex in mammals.
TnA receives olfactory input(Reiner and Karten 1985, Swanson and
Petrovich 1998), hippocampal and hypothalamic output (Casini, Bingman et
al. 1986, Canteras, Simerly et al. 1995, Cheng, Chaiken et al. 1999),
enrichment in androgen and estrogen receptors (Martinez‐Vargas, Stumpf
et al. 1976, Balthazart, Foidart et al. 1992, Balthazart, Foidart et al.
1998, Bernard, Bentley et al. 1999) and plays a tole in sexual behaviors
(Thompson, Goodson et al. 1998, Cheng, Chaiken et al. 1999, Absil,
Braquenier et al. 2002) as well as mammals so it specifically comparable
to the mammalian medial nucleus of the amygdala (MeA). Nucleus taeniae
of the amygdala (TnA) in birds responded to sounds and calls thus,
amygdala plays role in vocalization..(Fujii, Ikebuchi et al. 2016)
SpA is comparable to extended amygdala (EXA) in mammalia since they have
a similar location (ventral to globus pallidus (GP)).(Kitt and Brauth
1981, Martin Wild, Arends et al. 1990, Roberts, Hall et al. 2002,
Reiner, Perkel et al. 2004) .(Yamamoto, Sun et al. 2005)
The amygdala of mammals influences physiological functions, and
emotionally-laden social behavior (Aggleton 1992). The amygdala’s
intricate networks of sensory inputs, motor outputs and interneurons
mediate these vital functions. Afferent inputs to the amygdala contains
monosynaptic projections from the olfactory bulb, subcortical sensory
pathways, and hippocampal and other cortical connections (Ottersen 1982,
Russchen 1982). The amygdala in mammals has a unique location for rapid
detection and appraisal of events in the immediate environment That is
important for rapid cognitive to respond swiftly in a life and death
situation.(Cheng, Chaiken et al. 1999)
In rats lateral amygdala neurons respond to fear (LeDoux, Cicchetti et
al. 1990). they also have some neurons that can vocalize different
frequencies used possibly for different ends (Parsana, Li et al. 2012).
In bats, the neurons in the lateral (Gadziola, Grimsley et al. 2011) or
basolateral amygdala (Gadziola, Grimsley et al. 2011, Naumann and Kanwal
2011, Gadziola, Shanbhag et al. 2015) respond selectively to specific
social calls. Furthermore, the arcopallium in birds can also respond to
vocal sounds.
Subdivision structures and corresponding function of amygdala in avian
and mammals are probably evolve in different ways.(Fujii, Ikebuchi et
al. 2016)
In primates, amygdala appears almond shaped and is located in the
anterior temporal lobe, toward its medial side. It receives projections
from most cortical fields (Herzog and Van Hoesen 1976, Aggleton, Burton
et al. 1980, Turner, Mishkin et al. 1980, Mufson, Mesulam et al. 1981,
Friedman, Murray et al. 1986, Stefanacci and Amaral 2000), and usually
returns them (Avendan, Price et al. 1983, Amaral and Price 1984,
Carmichael and Price 1995, Ghashghaei and Barbas 2002). These anatomical
facts, show the pivotal position of the amygdala in the
telencephalon.(Murray 2007).