Rapid acquisition of intrinsic signal cortical maps using periodic stimulation
University of California, San Francisco
Conventional methods for data acquisition and analysis of the intrinsic signal optical responses are based on episodic presentation of stimuli. E.g., for construction of the orientation map of V1 one collects images while presenting a moving square grating of one orientation followed by a blank screen for relaxation of the response, after which the sequence is repeated for another randomly chosen orientation. These transient responses to the different orientations are averaged and normalized by the response to a "blank" stimulus (or to the average "cocktail blank" response to the entire stimulus set) to produce the map of the cortical response to a given orientation.
We present a new technique for acquiring intrinsic signal optical images which uses continuous stimulus presentation and data acquisition. The main idea is to present a temporally periodic stimulus and to analyze the component of the response at the stimulus frequency, analogous to steady-state evoked potentials. The advantages of this method include the removal of the heart and respiration rate artifacts, since the frequency of the stimulus is purposely chosen far from the artifact frequencies, and a dramatic reduction in acquisition time, due to absence of the blank relaxation periods and the initial latencies of each optical response.
To demonstrate the technique we present results on retinotopy of mouse visual cortex. Such maps can be obtained in as little as 20 minutes. (Supported by the Sloan and Swartz Foundations).