Loulwa Reda, Office of Communications, email@example.com
Will we ever be able to fully understand the brain cells and the process of learning in humans? We know that human brains harbor over 80 billion neurons, each of which are chemically and electrically connected with up to 10,000 others, resulting in the worlds’ most complex network.
But how exactly does it work? How are memories stored in our brain? How do we learn different languages and musical instruments? These are questions that scientists are still grappling with, and the pursuit for understanding how learning and memory works in the brain remain one of toughest pursuits in neuroscience. Despite some significant advancements in that direction, we still do not have answers to most, if not all of them.
While the widely accepted concept of "synaptic plasticity" is considered to be the cellular correlate of learning and memory, this theory fails to explain a large set of questions on the nature of the memory and the mechanisms of learning. The study conducted by Daou and Margoliash used the mating songs of the zebra finch bird to show how intrinsic (rather than synaptic) properties of neurons are closely tied to the process of learning. The study touches the basis of learning and memory in species that have a brain and memory and are able to learn.
“The songbird is the best system for this study because these species learn how to vocalize from their parents almost exactly as humans learn how to speak from their parents,” said Daou. “The similarity between humans and songbirds in vocal communication is remarkable.”
In this study, zebra finches’ songs were recorded on daily basis and their vocalizations were analyzed via dedicated software that extract various features in their sounds such as amplitude, pitch, and frequency modulation. These aforementioned features are not innate in songbirds, but rather learned throughout development. Daou and Margoliash were able to prove how the intrinsic properties of cells covary across life, rapidly and dynamically relating to learned features of individual zebra finches’ songs. According to Daou, birds that were taught by the same tutor or parent had not only very similar songs but also strikingly similar intrinsic cell properties. Siblings that learnt from their father the same exact song, had the same exact intrinsic properties of their neurons. This is the first result that strongly and directly relates cellular properties in the "cortex" of songbirds to behavioral changes and measures.
Having recorded the songs of different bird groups, the researchers then used a mathematical model to fit their collected intracellular data to the model parameters, and then used the model to compare how the intrinsic properties of these birds varied, showing a striking within-bird homogeneity and across-birds heterogeneity that were strongly correlated with similarities in songs across birds.
Vocal control and learning are critically dependent on auditory feedback in both songbirds and humans. To check for that, Daou implanted piezoelectric accelerometers on the skulls of songbirds to induce continuous delayed auditory feedback (cDAF), a technique that’s known to induce stuttering in humans as well as songbirds. This caused the birds to alter their song pattern in a way which was very similar to stuttering in humans. “By using this technique, we are able to alter vocalizations in birds and induce stuttering through experimental manipulations.,” Daou continues. It was surprising to see that the similarities in intrinsic properties degraded swiftly after cDAF exposure, hinting for the first time for a neural basis of stuttering.
Social cues modulate the performance of communicative behaviors in songbirds (as well as humans), and such changes can make the communication signal more salient. For example, male zebra finches are known to sing better melodical and more complex songs to get the attention of the female finch for mating. When the male finch is singing mating songs, the brain is much more “intricate,” their songs exhibit less “jitter” and are more stereotyped.
Throughout the research, the scientists were also able to find out that certain species of mice also learn through vocalization. This means that we may finally be on the verge of what many believe is a revolution in our understanding of human memory and learning.
Daou believes that we could, by following a developmental trajectory, intervene to primarily enhance the learning ability and memory in humans and then hopefully also find a cure to stuttering. This would help us learn how listening to speech when we are young allows us to shape the way we hear and speak for the rest of our lives, which is one of Daou’s main research interests and this study puts his goal in understanding these processes closer.
“Our next step is trying to figure out if learning in mice follows the same paradigm of songbirds. If this is true, this would enable us to alter how memory is coded in ways that we have never dreamt of,” he ended.