Both elegant and insightful, this is a beautiful piece of science.
On December 10, 2009, Dr. Allison J. Doupe from the University of California, came to the University of Western Ontario to give a talk about how songbirds can help us learn about the human brain.
In humans (as well as in various other animals such as bats, birds, and marine mammals), speech is learned through listening to the sounds made by those around us. In essence, humans are auditory learners. Learning speech is comprised of three parts. Firstly, there is the sensory experience: in essence, the sensation of experiencing sounds, or what we hear. Secondly, there is the trial-and-error phase, during which we make sounds ourselves in an attempt to mimic what we have heard. Finally, there is the phase where we learn to choose the correct sounds and ultimately produce coherent speech. For the first two stages to occur, hearing is essential.
Interestingly enough, birds also use this general pattern of learning. In addition to this similarity, birds also have areas in the brain devoted to learning speech. Major regions in the brain are called nuclei. The main pathway for speech production in birds requires four nuclei, and another three are present to aid in the learning process. There is also an auditory system used to store songs. It has also been shown that the cortical basal ganglia system (containing dopamine inputs) is specialized in birds for song. The importance of this resides in the results of damage to this region. Problems here can cause results analogous to those in humans. This area of the brain is required for normal speech production and sequesters behaviour. Furthermore, it is damaged in many disease states.
Songbirds have a region in the brain called LMAN that is part of the cortical pathway. This region is very active during song, and if damaged while the bird is learning a song, the learning stops, and the song is therefore truncated.
For example:
If this represents the song that an adult bird sings, then damage to LMAN during learning may cause the following:
Notice the order is correct, but it is shorter.
Neurons from LMAN send different signals at different frequencies. It is apparent that the activity observed in LMAN is altered due to the presence of a female though the song is still similar. In addition to this, seizure-like activity is seen when the bird is alone. Though the songs are similar, they are not the same. When the song is directed (towards a female) it is almost perfect, but when the bird is on its own, there are subtle variations in song. It is as if the birds are choosing the best version of the song when in solitude. This kind ofsong alteration is dependent on social situations. Variation may be attributed to a region called MAN, because when this area is turned off, singing improves.
Varying the outcome of the song aids the learning process. Variability is generated by the brain in songbirds and has structure. Juvenile birds have more variability than adults, since they are ”practicing” their song. In terms of social relevance, females prefer directed songs; that is to say, songs with less variability. However, they do prefer unfamiliar songs if the song is indeed directed. Interestingly enough, juvenile birds’ songs are more directed when in the presence of a female.
There are some more regions associated with variability as well as song learning, including Area X and DLM. Any auditory input will travel in the following sequence: Area X –> DLM –> LMAN. Neurons in DLM increase in firing rate, and this influences LMAN. If Area X is lesioned (that is to say, its function is removed), the bird cannot stabilize the song, but it is not truncated. This means that all the elements exist, but they are repeated or out of order. Normally, Area X is active and DLM is inhibited, but the neurotransmitter GABA inhibits Area X and this activates DLM. LMAN has a basal firing rate (is constantly firing neurons at low levels), but its activity is abnormal without Area X.
Finally, pauses within firing patterns have been observed. These pauses are more prevalent in undirected songs, but they correspond to the nature of the song. There seems to be a correlation betweenthe pauses and the level of direction in the song.
Although there is still much needed before we can fully understand how a bird produces its song, and more still before we can appreciate the complex molecular acrobatics involved in human speech formation, the ongoing research gives us much reason for excitement.
For more information please visit Dr. Allison J. Doupe’s website:
