Barrel cortex: What is it good for?

The rodent whisker system, with barrel cortex as its most prominent structure, has evolved into a powerful model system to study sensory processing. However, despite the vast amount of data collected on barrel cortex neural activity patterns, as well as its circuitry and plasticity, the precise behavioral and cognitive operations for which this structure is needed are still elusive. Proposed functions of barrel cortex include detection, discrimination, coordination of whisker movements during exploratory locomotion or active touch, and associative learning. Departing from a definition of what exactly constitutes a function and how the involvement of a brain area in a specific task can be established conclusively, we here review the arguments suggesting barrel cortex is involved in either of these functions. We conclude that currently available data do not unequivocally support a crucial role of barrel cortex in core sensorimotor functions like sensory processing for detection and discrimination or motor processing for movement. Instead, it appears that barrel cortex' contribution to behavior becomes ever more critical for performance with increasing cognitive load. We argue that our ignorance about barrel cortex' involvement in behavior is partly due to the lack of basic experiments employing permanent lesioning of the barrel field, as well as neglect of procedural parameters determining cognitive load in behavioral tasks. It is our belief that close attention to these factors in future experiments will help to eventually discover what barrel cortex is actually good for.