Here's how we have eyes in the back of our heads

Washington : Boffins have identified two classes of brain cells with distinct roles in visual attention, and highlighted mechanisms by which these cells mediate attention in a manner that allows us to fix our gaze on one object while independently directing attention to others.

Researchers led by Jude Mitchell, at the Salk Institute conducted experiments on primates who learned to play sophisticated video game, which challenged their visual attention-focusing skills.

The study recorded electrical activity from almost 200 different neurons in part of the visual cortex that has been implicated in mediating visual attention, and examined how each neuron’s response changed when attention was directed to the stimulus in its receptive field.

Researchers found that the neurons responded when a stimulus appeared within a window known as the neuron’s ‘receptive field, which covers a small part of the visual field that the eye sees.

Whenever the stimuli entered the neuron’s receptive field, the cell produced a volley of electrical spikes, known as ‘action potentials’.

The study noted that different neurons produced different shaped electrical spikes: ‘broad spikes’ and ‘narrow spikes’.

Earlier studies have 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 inter-neurons evoke narrow spikes. These neurons only connect to their local neighbouring neurons, and are involved in local computations.

The researchers after sorting the neurons by waveform observed 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, on the other hand, were less influenced by attention. Some fired faster, while others fired more slowly when attention was directed to the stimulus in the receptive field.

"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," Mitchell said.

"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,” he added.

The findings of the study were published in the July issue of Neuron. (ANI)