Introducing the brain: neuronal connections are ordered (Introduction)

by David Turell , Friday, October 14, 2022, 17:17 (769 days ago) @ David Turell

A new discovery:

https://medicalxpress.com/news/2022-10-secret-wiring-diagram-brain.html

"In the brain, our perception arises from a complex interplay of neurons that are connected via synapses. But the number and strength of connections between certain types of neurons can vary. Researchers...have now discovered that the structure of the seemingly irregular neuronal connection strengths contains a hidden order. This is essential for the stability of the neuronal network.

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"However, each synapse is unique and its strength can vary over time. Even experiments that measured the same type of synapse in the same brain region yielded different values for synaptic strength. However, this experimentally observed variability makes it difficult to find general principles underlying the robust function of neuronal networks," says Prof. Tatjana Tchumatchenko,

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"In the primary visual cortex (V1), the visual stimuli transmitted by the eye via the thalamus, a switching point for sensory impressions in the diencephalon, are first recorded. The researchers took a closer look at the connections between the neurons that are active during this process. To do this, the researchers measured experimentally the joint response of two classes of neurons to different visual stimuli in the mouse model. At the same time, they used mathematical models to predict the strength of synaptic connections. To explain their lab-recorded activities of such network connections in the primary visual cortex, they used the so-called "stabilized supralinear network" (SSN).

"'It is one of the few nonlinear mathematical models that offers the unique possibility to compare theoretically simulated activity with actually observed activity," says Prof. Laura Busse, research group leader at LMU Neurobiology. "We were able to show that combining SSN with experimental recordings of visual responses in the mouse thalamus and cortex allows us to determine different sets of connection strengths that lead to the recorded visual responses in the visual cortex."

"The researchers found that there was an order behind the observed variability in synapse strength. For example, the connections from excitatory to inhibitory neurons were always the strongest, while the reverse connections in the visual cortex were weaker. This is because the absolute values of synaptic strengths varied in the modeling—as they had in the earlier experimental studies—but nevertheless always maintained a certain order. Thus, the relative ratios are crucial for the course and strength of the measured activity, rather than the absolute values.

"'It is remarkable that analysis of earlier direct measurements of synaptic connections revealed the same order of synaptic strengths as our model prediction based on measured neuronal responses alone," says Simon Renner, Ph.D., of LMU Neurobiology, whose experimental recordings of cortical and thalamic activity allowed characterization of the connections between cortical neurons.

"'Our results show that neuronal activity contains much information about the underlying structure of neuronal networks that is not immediately apparent from direct measurements of synapse strengths. Thus, our method opens a promising perspective for the study of network structures that are difficult to access experimentally," explains Nataliya Kraynyukova, Ph.D."

Comment: it is not surprising to find a pattern of order in the brain. Neuronal activity must have a basis of designed organization.