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Medicineworld.org: Paying attention to attention

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Paying attention to attention




Paying attention to attention
Every kid knows that moms have eyes in the back of their heads. We are adept at fixing our gaze on one object while independently directing attention to others. Salk Institute neurobiologists are beginning to tease apart the complex brain networks that enable humans and other higher mammals to achieve this feat.

As per a research findings reported in the July 5, 2007 issue of Neuron, the scientists report two classes of brain cells with distinct roles in visual attention, and highlight at least two mechanisms by which these cells mediate attention. This study represents a major advance in our understanding of visual cognition, because it is the first study of attention to distinguish between different classes of neurons, says system neurobiologist John Reynolds, Ph.D., associate professor in the Systems Neurobiology Laboratory at the Salk Institute.

In the experiments, animals learned how to play a sophisticated video game, which challenged their visual attention-focusing skills. During the game, the Salk scientists recorded electrical activity from individual neurons in part of the visual cortex that has been implicated in mediating visual attention. (Please see video.).

http://www.snl.salk.edu/~jude/attentiontask.avi.

As illustrated in the demonstration, the neurons respond when a stimulus appears within a window (indicated by the circle) covering a small part of the visual field that the eye sees. This window is known as the neurons receptive field. Whenever the stimuli entered the neurons receptive field, the cell produced a volley of electrical spikes, known as action potentials, indicated by vertical tick marks in the demonstration.

On some trials, attention was directed to the stimulus that entered the neurons receptive field, while on other trials attention was instead directed to the other stimuli. The scientists recorded almost 200 different neurons, and examined how each neurons response changed when attention was directed to the stimulus in its receptive field.

They observed that neurons typically responded more strongly when attention was directed to the stimulus in their receptive fields. Upon closer inspection, however, the scientists noticed that different neurons produced different shaped electrical spikes: broad spikes and narrow spikes. Other scientists had previously identified two different types of neurons that produce these two waveforms. The most common neuron type, called a pyramidal cell, produces broad spikes. These neurons transmit signals between different brain areas. The other class, fast-spike interneurons evoke narrow spikes. These neurons only connect to their local neighboring neurons, and are involved in local computations.

After sorting the neurons by waveform, the scientists found that attention had different effects on the two different types of neurons. The narrow-spiking cells typically fired more frequently when the tracked object was attended than when it was unattended. Broad-spiking cells, conversely, were less influenced by attention. Some fired faster, while others fired more slowly when attention was directed to the stimulus in the receptive field. Whats more, attention caused the stream of spikes produced by the narrow-spiking neurons to be much more reliable.

"By distinguishing among the different neural elements that make up the cortical circuit, we are gaining a view of the biological underpinnings of attention that is unprecedented in its level of detail," says post-doctoral researcher Jude Mitchell, Ph.D., lead author on the study. He adds that, while there is much more work ahead, "if we can understand how attention is acting on different cell classes, this will significantly improve our understanding of the pathology of neurological diseases in which attention is impaired".


Posted by: Daniel    Source




Did you know?
Every kid knows that moms have eyes in the back of their heads. We are adept at fixing our gaze on one object while independently directing attention to others. Salk Institute neurobiologists are beginning to tease apart the complex brain networks that enable humans and other higher mammals to achieve this feat.

Medicineworld.org: Paying attention to attention

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