Author Topic: [AUS] [attn druggies: :)] How the brain enables us to rapidly focus attention  (Read 82 times)

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source: https://qbi.uq.edu.au/article/2018/12/how-brain-enables-us-rapidly-focus-attention

How the brain enables us to rapidly focus attention

QBI researchers have discovered a key mechanism in the brain that may underlie our ability to rapidly focus attention.

Our brains are continuously bombarded with information from the senses, yet our level of vigilance to such input varies, allowing us to selectively focus on one conversation and not another.

Professor Stephen Williams of the Queensland Brain Institute at UQ explains, “If we want to give our full concentration, something happens in the brain to enable us to focus and filter out distractions.”

“There must be a mechanism that signals the thing we want to focus on.”

However, this mechanism is not well understood, he says.



Research has shown that the electrical activity of the neocortex of the brain changes, when we focus our attention. Neurons stop signalling in sync with one another and start firing out of sync.

This is helpful, says Williams, because it allows individual neurons to respond to sensory information in different ways. Thus, you can focus on a car speeding down the road or on what a friend is saying in a crowded room.

It’s known that the cholinergic system in the brain plays an important role in triggering this desynchronisation.

The cholinergic system consists of clusters of special neurons that synthesise and release a signalling molecule called acetylcholine, he explains, and these clusters make far reaching connections throughout the brain.

Not only does this cholinergic system act like a master switch, but mounting evidence suggests it also enables the brain to identify which sensory input is the most salient – i.e. worthy of attention – at any given moment and then shine a spotlight on that input.

“The cholinergic system broadcasts to the brain, ‘this thing is really important to be vigilant to’,” says Williams.

He adds that the cholinergic system has been proposed to have a far-reaching impact on our cognitive abilities.

“Destruction of the cholinergic system in animals profoundly degrades cognition, and the formation of memory,” he says.

“Importantly, in humans a progressive degeneration of the cholinergic system occurs in devastating diseases that blunt cognition and memory, such as Alzheimer’s disease.”

But precisely which neurons in the cortex are being targeted by this master switch and how it’s able to influence their function was unknown.

Williams and QBI researcher Lee Fletcher wondered if layer 5 B-pyramidal neurons, the ‘output’ neurons of the neocortexWiki, might be involved, because they are intimately involved in how we perceive the world.

“The output neurons of the neocortex perform computations that are thought to underlie our perception of the world,” says Williams.

Williams and Fletcher wanted to know if the cholinergic system is able to influence the activity of these output neurons.

Using a technique called optogeneticsWiki, they modified neurons in the cholinergicWiki system in the brains of mice so that they could be activated with a flash of blue light, triggering a sudden release of acetylcholine.

This allowed the researchers to closely monitor the interaction between the cholinergic system and the output neurons.

They discovered that if the output neurons were not currently active, not much happened.

But when those neurons received excitatory input to their dendrites, the cholinergic system was able to massively increase their activity.

 “It’s as if the cholinergic system has given a ‘go’ signal,” says Fletcher, enabling the output neurons of the neocortex to powerfully respond.

Importantly, this change was selective, and only apparent when excitatory input was being processed in the dendrites of the ‘output’ neurons.

“We have known for some time that the dendrites of the output neurons of the neocortex only become active when animals are actively performing a behaviour, and that this activity is correlated with perception and task performance,” says Williams.

This new work demonstrates that the cholinergic system is critical to this transition in mice and rats, allowing the output neurons to perform computations in a state-dependent manner.

We suggest that this switch also occurs in the human neocortex, allowing us to rapidly switch our state of vigilance and attention,” says Williams.

“Our work therefore provides important insight into how the progressive degeneration of the cholinergic system in disease blunts human cognition.”

The findings “A dendritic substrate for the cholinergic control of neocortical output neurons” are published in the journal Neuron.

--- --- --

Layer 2/3 pyramidal neurons are organized around the central core of layer 5 apical dendrites, and stronger connections between layer 2/3 pyramidal neurons and L5B pyramidal neurons may exist within the same cluster (Thomson and Bannister, 1998; Reyes and Sakmann, 1999) Oct 24, 2007

see Synaptic Connections between Layer 5B Pyramidal Neurons in Mouseat www.jneurosci.org/content/27/43/11473 (some excerpts are below:)

Synaptic Connections between Layer 5B Pyramidal Neurons in Mouse Somatosensory CortexWiki Are Independent of Apical Dendrite Bundling

The somatosensory cortex receives all sensory input from the body. Cells that are part of the brain or nerves that extend into the body are called neurons. Neurons that sense feelings in our skin, pain, visual, or auditory stimuli, all send their information to the somatosensory cortex for processing (ie. perceptionWiki)



Cell clusters forming dendritic bundles.

A, Two-photon image from a living slice showing L5B pyramidal cells arranged in cell clusters and with bundling apical dendrites. Cells labeled with the same color asterisks are in the same cluster.

B, Cells were filled through the patch pipette with a red fluorescent dye (Alexa Fluor 594) to mark the recorded cell and to confirm apical dendrite branching pattern. Two patch pipettes are shown recording from cells located in two different clusters.

C, Images from A and B superimposed. Recordings were made from five different cells located in four different clusters (the 2 cells to the left are in the same cluster).

Abstract

Rodent somatosensory barrel cortex is organized both physiologically and anatomically in columns with a cross-sectional diameter of 100–400 μm.

The underlying anatomical correlate of physiologically defined, much narrower minicolumns (20–60 μm in diameter) remains unclear.

The minicolumn has been proposed to be a fundamental functional unit in the cortex, and one anatomical component of a minicolumn is thought to be a cluster of pyramidal cells in layer 5B (L5B) that contribute their apical dendrite to distinct bundles.

In transgenicWiki mice with fluorescently labeled L5B pyramidal cells, which project to the pons and thalamus, we investigated whether the pyramidal cells of a cluster also share functional properties.

We found that apical dendrite bundles in the transgenic mice were anatomically similar to apical dendrite bundles previously proposed to be part of minicolumns.

We made targeted whole-cell recordings in acute brain slices from pairs of fluorescently labeled L5B pyramidal cells that were located either in the same cluster or in adjacent clusters and subsequently reconstructed their dendritic arbors.

Pyramids within the same cluster had larger common dendritic domains compared with pyramids in adjacent clusters but did not receive more correlated synaptic inputs.

L5B pyramids within and between clusters have similar connection probabilities and unitary EPSP amplitudes. See Excitatory postsynaptic potentialWiki.

(The flow of ions that causes an EPSP is an excitatory postsynaptic current (EPSC). EPSPs, like IPSPs, are graded (i.e. they have an additive effect). When multiple EPSPs occur on a single patch of postsynaptic membrane, their combined effect is the sum of the individual EPSPs.)

Furthermore, intrinsically bursting and regular spiking pyramidal cells were both present within the same cluster. In conclusion, intrinsic electrical excitability and the properties of synaptic connections between this subtype of L5B pyramidal cells are independent of the cell clusters defined by bundling of their apical dendrites.

Results

Characterization of bundles formed by apical dendrites of layer 5B pyramidal neurons
In transgenic mouse lines (CLM-1 and CLM-11) expressing the chloride-sensitive fluorescent protein Clomeleon, we observed a pattern of vertically ascending apical dendrites originating from clustered L5B pyramidal neurons.

In transgenic mouse lines (CLM-1 and CLM-11) expressing the chloride-sensitive fluorescent protein ClomeleonWiki, we observed a pattern of vertically ascending apical dendrites originating from clustered L5B pyramidal neurons (Fig. 1A,B).

A vertical organization of apical dendrites organized in bundles has previously been described in fixed tissue in the somatosensory cortex of mice (Escobar et al., 1986; White and Peters, 1993) and in other species and cortical areas (Peters and Walsh, 1972; Peters and Sethares, 1991; Peters and Yilmaz, 1993; Schmolke and Künzle, 1997; Rockland and Ichinohe, 2004; Buxhoeveden and Casanova, 2005). Bundles were clearly visible with two-photon microscopy in vivo (Fig. 1A) (Helmchen and Denk, 2005) and in the acute living brain slice (Fig. 1B).

The fluorescent labeling enabled the visualization of dendrite bundles extending from deep layer 5 to the pialWiki surface.

Bundle-forming cells were classified as L5B pyramidal neurons based on their location in the cell-dense lower part of layer 5 (mean distance from pia, 739 μm) and the extensive branching and spread of their apical dendrite tuft (see Figs. 6, 7) (Markram, 1997; Markram et al., 1997; Schubert et al., 2001; Manns et al., 2004).



Figure 1.

Two-photon excitation images from neocortex showing fluorescent layer 5B pyramidal cells with bundling apical dendrites.

A, Dendritic bundles in motor cortex were visualized with in vivo two-photon microscopy.

B, Fluorescently labeled layer 5B pyramidal neurons located in cell clusters with apical dendrites extending in bundles were also visualized with two-photon microscopy in the acute somatosensory cortex slice used for electrophysiological recordings.


It has been suggested that pyramidal neurons within a minicolumn are more densely interconnected, have larger EPSPs, and receive common inputs .

this continues at the source link ...



The somatosensory cortex is highlighted in red in the brain

for more on Somatosensory Cortex: Definition, Location & Function see https://study.com/academy/lesson/somatosensory-cortex-definition-location-function.html

some excerpts follow:

What the fuck is the Somatosensory Cortex ?

Have you ever wondered if you feel things the same way other people do? How do you know 'red' is really the same red to everyone? Maybe the person next to you sees green as red… These thought-provoking questions can't be answered precisely with science, but we can learn more about how external stimuli, like colors, are processed in the brain.

This is where the somatosensory cortex comes in. This part of the brain processes sensations, or external stimuli, from our environment. Before we learn more about the somatosensory cortex, we need to learn a little bit about brain anatomy and where the somatosensory cortex is located.

Where the fuck is it located ?

The brain is the control center of the whole body. It is made up of a right and left side, or lobes, which are connected in the middle by the corpus colossum. Each lobe is devoted to a different function. The outer layer of the brain is called the cerebral cortex.

Think of it like the skin on a fruit, the skin is the cerebral cortex, and the fruit is the white insides of the apple. The cerebral cortex helps with processing and higher order thinking skills, like reasoning, language, and interpreting the environment. This image shows a cross section of the brain, with the cerebral cortex shown as the dark outline.

The somatosensory cortex is a part of the cerebral cortex and is located in the middle of the brain. This image shows the somatosensory cortex, highlighted in red in the brain.

The somatosensory cortex receives all sensory input from the body. Cells that are part of the brain or nerves that extend into the body are called neurons. Neurons that sense feelings in our skin, pain, visual, or auditory stimuli, all send their information to the somatosensory cortex for processing. The following diagram shows how sensations in the skin are sent through neurons to the brain for processing.

The skin transmits signals through other neurons to the brain sensory to brain pathway.

Each neuron takes its information to a specific place in the somatosensory cortex. Next, that part of the somatosensory cortex gets to work on figuring out what the information means.

Think of it like this:

Like scientists sending data to a data analyst.

Each scientist, like the neuron, gathers information and sends it to a master analyzer or the somatosensory cortex.

Some neurons are very important and a big chunk of the somatosensory cortex is devoted to understanding their information.

The senior scientist sends the most important information to our analyst, and he spends a lot of time understanding it.

However, our junior scientists or volunteers gather less important information, so our analyst, or somatosensory cortex, spends less time on that data.
« Last Edit: July 06, 2019, 12:32:12 PM by Chip »
Over 90% of all computer problems can be traced back to the interface between the keyboard and the chair !

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