Late Latency Response (LLR) Testing
Late Latency Response (LLR) is a component of auditory evoked potential response. The auditory evoked potential represents the cortical activity related to memory, attention, and auditory discrimination proficiency. The processing of acoustic signal occurs differently between verbal and non-verbal stimuli. These influence the amplitude and latency patterns.
The LLR response is found between 50 to 250 milliseconds from the time of stimulation. The test reflects the response of auditory cortex. LLR can acquire through pure tone stimulation by applying an envelope tone buster. The response is from a low frequency less than 30 Hz and has a frequent voltage of ranging between 3 to 10 microvolt’s.
The recordings have certain high points and low points. The peak depicts positive potential difference those are labelled as ‘P’ where as the low points depicts negative potential difference those are labelled as ‘N’. LLR responses are usually acquired by surface electrodes.
Why to take LLR test?
Late Latency Response test is used to diagnose certain conditions in auditory. This method of testing is very helpful in providing helpful information regarding hearing loss in patients with specific type of hearing disorder like with ‘c’ frequency. The LLR test can also help in testing the presence of nervous system abnormalities specifically above auditory brainstem levels.
How to prepare yourself?
The patient is laid in a comfortable position and silent environment, preferably in a sound booth. The patient is instructed to relax or go to sleep during testing. Do not take any form of drugs those can affect nervous system.
What to expect?
Four electrodes are connected on the patient at right ear, left ear, upper forehead, and on lower forehead. Then the electrodes are connected to the computer to record the responses.