Humans and other primates have an extraordinary ability to voluntarily and efficiently focus attention on important information while ignoring distraction. For decades it has been hypothesized that this ability relies on the evolutionary expansion of the lateral prefrontal cortex, a part of the brain located in the lateral convexity of the frontal lobe, that reaches its highest level of complexity in primates.
Several studies have demonstrated that the activity of single neurons in the lateral prefrontal cortex of behaving primates is strongly modulated by allocating attention to different objects or locations. However, one fundamental question in this field of research is whether assemblies of simultaneously active lateral prefrontal cortex neurons (neuronal assembly) can generate sufficient information to implement the cognitive operation of attention. This is not trivial since when multiple neurons are simultaneously active the amount of information they generate depends on processes such as correlated noise and trial-to-trial response variability, which can substantially impair the information carried by a neuronal population.
In order to investigate this issue Martinez-Trujillo and his team recorded the activity of hundreds of lateral prefrontal neurons in non-human primates while they allocated attention to one of several objects across the visual field using a 4×4 millimeters microelectrode array chronically implanted on the brain surface. They input the recorded signals into a machine-learning algorithm running on a personal computer that mimicked the computations performed by a brain network of interconnected neurons. They tested the hypothesis that the computer will reliably signal where the subjects allocated attention on a computer display.
Indeed, the machine could predict with less than half a second resolution where the subjects directed attention on the display. This prediction was made well in advance the subjects executed any action towards the attended object. Thus, assemblies of prefrontal neurons can reliably signal the allocation of attention.
Importantly, subtly manipulating the correlated activity and therefore the functional interactions between the recorded neurons significantly altered the performance of the machine at focusing attention. This demonstrates that interactions between neurons in the lPFC play a fundamental role in the amount of information neuronal assemblies can encode.
These results are highly relevant across several disciplines including Neuroscience, Psychiatry, and Neurology. They demonstrate that the primate lateral prefrontal cortex plays a fundamental role in implementing the cognitive function of attention. They further indicate that inability to focus attention, as seen in patients with ADHD, Autism and Schizophrenia, may originate from subtle changes in the microstructure of the lateral prefrontal network that modulate the way individual neurons interact with one another. Importantly, because the machine could robustly decode the allocation of attention over multiple weeks, these findings open new venues for the emerging field of cognitive neuroprosthetics. It shows that brain signals can be extracted from the lateral prefrontal cortex using chronically implanted microelectrode arrays for a brain machine interface to “read out” a subject’s intentions well in advance of a motor action toward a desired goal, e.g., reaching grasping or moving toward an object. This can potentially improve the performance of existing neuroprosthetics using brain signals to drive mechanical devices that aid patients with paralysis.
This work was conducted by Sebastien Tremblay, a McGill University graduate student in Dr. Martinez Trujillo’s lab. Dr. Florian Pieper from the University of Hamburg, and Dr. Adam Sachs, a neurosurgeon from the Ottawa Hospital play fundamental roles in the project. Dr. Martinez-Trujillo is currently a professor at the Department of Physiology at McGill University (Quebec) and an associate Professor and scientist at the Robarts Research Institute at Western University (Ontario).
Source of text: Dr. Martinez-Trujillo
Original Research Article:
Attentional Filtering of Visual Information by Neuronal Ensembles in the Primate Lateral Prefrontal Cortex
Sébastien Tremblay, Florian Pieper, Adam Sachs, Julio Martinez-Trujillo
DOI: http://dx.doi.org/10.1016/j.neuron.2014.11.021
A video abstract is available on the journal website
http://www.cell.com/neuron/abstract/S0896-6273%2814%2901073-3
