Introducing the brain: another way neurons relate (Introduction)

by David Turell , Tuesday, November 19, 2024, 15:02 (1 day, 18 hours, 56 min. ago) @ David Turell

Using calcium, not sodium:

https://www.sciencealert.com/a-first-of-its-kind-signal-has-been-detected-in-human-brai...

"By measuring the electrical activity in sections of tissue removed during surgery on epileptic patients and analyzing their structure using fluorescent microscopy, the neurologists found individual cells in the cortex used not just the usual sodium ions to 'fire', but calcium as well.

"This combination of positively charged ions kicked off waves of voltage that had never been seen before, referred to as a calcium-mediated dendritic action potentials, or dCaAPs.

***

"In neurons, the signal is in the form of a wave of opening and closing channels that exchange charged particles such as sodium, chloride, and potassium. This pulse of flowing ions is called an action potential.

"Instead of transistors, neurons manage these messages chemically at the end of branches called dendrites.

"'The dendrites are central to understanding the brain because they are at the core of what determines the computational power of single neurons," Humboldt University neuroscientist Matthew Larkum told Walter Beckwith at the American Association for the Advancement of Science in January 2020.

"Dendrites are the traffic lights of our nervous system. If an action potential is significant enough, it can be passed on to other nerves, which can block or pass on the message.

"This is the logical underpinnings of our brain – ripples of voltage that can be communicated collectively in two forms: either an AND message (if x and y are triggered, the message is passed on); or an OR message (if x or y is triggered, the message is passed on).

"Arguably, nowhere is this more complex than in the dense, wrinkled outer section of the human central nervous system; the cerebral cortex. The deeper second and third layers are especially thick, packed with branches that carry out high order functions we associate with sensation, thought, and motor control.

"It was tissues from these layers that the researchers took a close look at, hooking up cells to a device called a somatodendritic patch clamp to send active potentials up and down each neuron, recording their signals.

"'There was a 'eureka' moment when we saw the dendritic action potentials for the first time," said Larkum.

"To ensure any discoveries weren't unique to people with epilepsy, they double checked their results in a handful of samples taken from brain tumors.

"While the team had carried out similar experiments on rats, the kinds of signals they observed buzzing through the human cells were very different.

"More importantly, when they dosed the cells with a sodium channel blocker called tetrodotoxin, they still found a signal. Only by blocking calcium did all fall quiet.

"Finding an action-potential mediated by calcium is interesting enough. But modelling the way this sensitive new kind of signal worked in the cortex revealed a surprise.

"In addition to the logical AND and OR-type functions, these individual neurons could act as 'exclusive' OR (XOR) intersections, which only permit a signal when another signal is graded in a particular fashion.

"'Traditionally, the XOR operation has been thought to require a network solution," the researchers wrote.

"More work needs to be done to see how dCaAPs behave across entire neurons, and in a living system. Not to mention whether it's a human-thing, or if similar mechanisms have evolved elsewhere in the animal kingdom."

Comment: finding more complexity in neuron signaling is not surprising. Is it just ours or seen elsewhere Is an interresting question. Just ours would not surprise me.