However, a number of additional structures within the forebrain have been posited to be involved in or essential for consciousness--at the primary or possibly some higher level--in mammals.
In songbirds and parrots, which exhibit complexity of vocalization and communicative abilities, similar forebrain circuit loops involve the song and vocalization nuclei specific to these taxa (Wild, 1993, 1994; Vates et al., 1996; Striedter and Vu, 1998; Bottjer et al., 2000; Jarvis and Mello, 2000; Jarvis et al., 2000, 2002; Lavenex, 2000; Deng et al., 2001).
Further, just as in mammals, the large brain-body ratios in birds are in large part due to expansion of the forebrain, and specifically, the pallial association areas of the telencephalon--the nidopallium and mesopallium--which are most expanded in birds with high cognitive abilities, the psittacines (parrots) and passerines (which include corvids) (Lefebvre et al., 2004; Iwaniuk and Hurd, 2005).
Forebrain organization in amphibians is markedly different from that in reptiles, birds, and mammals, with the telencephalon characterized by having only a very small nonlimbic pallium situated between the medial (hippocampal) and lateral (olfactory) pallia (see Butler and Hodos, 2005).
Birds clearly have forebrain circuitry that, at least in some respects, is very similar to what is found in mammals.
Now, researchers express excitement about the possibility of using a natural hormone, nerve growth factor (NGF), to "rescue" a withering basal forebrain
and block the progression of at least some Alzheimer's symptoms.