VAPP and functional magnetic resonance imaging (fMRI)

VAPP was specifically designed with fMRI studies in mind.  VAPP was designed to return millisecond accuracy for long duration fMRI stimulus runs (e.g., eight to ten minutes).   What this means is that one can present the same stim file with the exact timing to multiple subjects again and again - knowing that VAPP will always present stimuli for exactly the same duration and for exactly the same total length of time - regardless of subject input.   Please see our publication list for a list of both blocked and event-related fMRI studies that have employed VAPP. 

VAPP was designed to work with a fiber-optic response device for fMRI.  The fiber-optic response device, now distributed commercially by Cold Switch Technologies,  is call the LumiTouch Reply system.  Contact Doug Broadfoot at dougb@lightwave-medical.com for more information.   The LumiTouch Reply system consists of two ergonomically designed hand held response pads - each with up to four buttons.  Testing of this device has indicated that there is absolutely no interference in the fMRI signal.  VAPP asynchronously records all LumiTouch key presses as 'event codes' in the VAPP log files.  These log files can then be easily parsed in Excel or other spreadsheet to quickly compute behavioral data.   In addition, if directed, VAPP will instantaneously echo all behavioral event codes (along with stimulus event codes) to CIRC for online monitoring of all behavior.   CIRC is a companion program that runs on a separate PC than VAPP and is designed to provide researchers with online display of individual trials and summary statistics (e.g. reaction times to target stimuli, number of false alarms).  CIRC also records a binary log file that can be subsequently parsed with MATLAB code (or other custom code) to output behavioral data for quick input into functional imaging analyses programs such as Statistical Parametric Mapping (SPM)

In order to facilitate perfect temporal synchronicity between VAPP (and CIRC) and the fMRI scanner, VAPP was designed to load all stimuli and then wait for a pulse from the scanner (outputted by most MRI scanners at the onset of the first radio frequency (rf) excitation) to initiate presentation of stimuli.  Using this protocol, VAPP and the scanner will be temporally synchronized to within one screen refresh (less than 15 ms on most video monitors).  

 It is important to note that some scanners may run on slightly different computer clocks than VAPP and CIRC .  That is, if one employs a TR (repetition time) of 2000 ms, that might actually be 2025 ms on the VAPP and CIRC clocks.  Thus, over the course of a ten minute fMRI stim run, VAPP, CIRC and the scanner will begin to diverge - sometimes quite extensively.   However, most MRI scanners will have ports that output signals or triggers every time rf is applied (i.e., every slice).  Using a custom made device, we take the scanner output (a negative pulse of 10 ms duration and 5 v amplitude on our GE scanner) and convert it to a user specified event code.  This conversion is done using what we affectionately refer to as the 'byte box'.  The byte box takes in the scanner rf signal and converts each pulse to an event code - this code is then plugged into CIRC and we have a record on CIRC when every slice was collected.   We can then parse the CIRC log file by behavioral conditions (e.g., hits, false alarms) and output - to the exact slice - when each event occurred.   For example, using this procedure we have been able to selectively isolate brain regions associated with making incorrect or erroneous responses - see Kiehl, Liddle and Hopfinger (2000).  Error processing and the rostral anterior cingulate: An event-related fMRI study.  Psychophysiology, 37, 216-223. Download pdf. See the VAPP publications area for more fMRI studies employing VAPP.

Custom 'byte boxes' can be obtained by contracting with us on a per group basis.   Cold Switch Technologies, makers of the fMRI fiber optic response device, the LumiTouch Reply system, will also build into the response devices the ability to interface scanner signals within the input from the response device.  Contact Doug Broadfoot at dougb@lightwave-medical.com for more information.