Important brain functions derive from the ways in which brain cells, or neurons are connected. The contact points between them are called synapses, and scientists seek to draw maps of synaptic connections that show not only what neurons are connected to what other neurons, but also how strong each connection is, this allows much better to understand the flow of thoughts and processes.
Although electronic microscopy has been used with great success to make visual maps of synaptic connections, these images lack information about the force of connections and, therefore, on the ultimate function of the neuronal network. Now, a team of Harvard scientists has cartographed and cataloged more than 70,000 synaptic connections of about 2,000 rats neuronsusing a silicon chip capable of registering small, but revealing synaptic signs of a large number of neurons.
The findings, published in Nature Biomedical Engineering, are a great advance in the neuronal registry and can help scientists be one step closer to drawing a detailed map of the synaptic connections of the brain And with that not only to deeply understand this organ, but also reproduce it.
The key to creating this map is to use a patch fixing electrode, the highest standard in terms of neuronal registration, which can effectively enter An individual neuron to record a weak synaptic signal with high sensitivity And, therefore, you can find a synaptic connection and determine its intensity.
Scientists have long tried to apply this high sensitivity intracellular record to a large number of neurons at the same time with the aim of measuring and characterizing a large number of synaptic signals and, thus, Draw a map noted with the intensities of the connections. But they have rarely gone beyond getting intracellular access to a handful of neurons at the same time.
The authors of the study, led by Donhee Ham and Elizabeth S. Armstrong, developed a series of 4,096 microaguase electrodes in a silicon chip, which made a massive intracellular record and parallel of rat neurons grown in the chip. From this, more than 70,000 synaptic connections of about 2,000 neurons were extracted. Which is equivalent to about 35 connections per neuron … Very little considering that each neuron can have up to 15,000 synapses, but without a doubt a step of giants.
Ham and Armstrong’s team used the chip to open neurons with Small current injections through electrodes in order to parallel their intracellular record. The microaguase design is similar to the patch fixing electrode, which is essentially a glass pipette that houses the electrode and has a hole at the end.
Looking in detail discovered that, On average, more than 3,600 microaguase electrodes of a total of 4,096 (that is, 90 %) were intracellularly coupled to the neurons from the top.
The number of synaptic connections that the equipment extracted from these intracellular registration data unprecedented from any The network increased to 70,000 plausible synaptic connections, compared to the approximately 300 of the previous models. The quality of the registration data was also better, which allowed the team to classify each synaptic connection based on its characteristics and strengths.
“One of the biggest challenges, after we achieved the massive intracellular record in parallel, was how to analyze the overwhelming amount of data -HAM concludes in a statement -. Since then we have traveled a long way to obtain information about synaptic connections from them. Now We are working on a newer design that can be implemented in a living brain. ”