Question:  Can the sleep estimation algorithms in the analysis software package be used to investigate daytime sleepiness?

Answer:  The sleep estimation algorithms in our software were validated for estimating sleep in a standard sleeping environment.  They have not been validated for naps or "micro-sleeps", which can take place during the course of the day.  The problem with actigraphic estimates of sleep is that one is dealing with a single channel of simple information.  It is impossible for the actigraph to distinguish between periods of extreme inactivity (reading, TV watching) and sleep during the course of the day.  What makes the nighttime estimates of sleep possible is the assumption that sleep is the intent during that period of time (based on event markings, logs, etc.).  With knowledge that the subject is in bed and TRYING to sleep, the estimates of sleep from activity can be used with much more confidence.
This does not mean that the actigraph cannot be used to examine daytime sleepiness; but one cannot say, with any certainty, that an inactive period is asleep.  Solution?  Don't report these periods as naps.  Don't report them as Micro-Sleeps.  Refer to them as daytime periods of inactivity.  Show that one group has more of these periods than another or that the patterns of same group change with intervention.  Let the reader draw his/her own conclusion.  Given enough subjects and a large enough change in the number and duration of these periods of inactivity the results can  be quite impressive,  especially when one considers that the more rigorous alternatives (portable EEG or videotaping) are much more difficult (if not impossible) in most populations.

Question: Why are there several data collection modes available in the various models of actigraphs available from AMI? 

Answer: Depending on the Mode of Operation selected, information derived from the conditioned analog signal is processed in different ways to provide information about the subject's motion. 

Question:  What’s a good way to characterize “quality of sleep” or sleep fragmentation?

Answer:  ActionW version 2 includes a statistic called "activity index," which is the percent of epochs with >0 activity score which is a good indicator of restlessness.  Also Action4 has the F.A.C.E. function, which is described below:

ACTION4 features F.A.C.E. (Frequency Analysis of Consecutive Epochs)
This technique is used to quantify the continuity vs. fragmentation of data within intervals of interest.  For example, the continuity of periods of inactivity may be displayed.  The user defines the criterion for inactivity, such as all epochs with a value of 1 or less.  The number of consecutive epochs of inactivity are counted for all periods of inactivity during an interval of interest.  The results are displayed as a plot of the cumulative total inactivity time (in percent) as a function of the consecutive epoch duration.  The median value for each analysis is reported as a numerical descriptor and is defined as that duration for which 50% of the time is spent in runs of this duration or less.

A “Bad” Night
Quickly rising curves indicate that most of the inactive epochs occur in short bursts.

A “Good” Night
Slowly rising curves indicate that most of the inactive epochs occur in longer chains.

ACTION3 defines SLEEP numerically as 1 and WAKE numerically as 0.  To use FACE to represent the runs of estimated wakefulness with the Time-in-Bed, set the THRESHOLD detection to BELOW (which is actually below or EQUAL to...) and the critical value to ZERO.

Question:  Will the Actigraph be fooled into thinking a subject is asleep if the device is simply removed?

Answer: No.  Because of the high sensitivity and precision calibration of the devices, periods of inactivity associated with sleep are easily differentiated from periods of inactivity caused by the device being removed.  In the example below, three instances where the actigraph was removed (other than the morning bathing period) are noted.  The first period noted is an entire night.
Additionally, since the Motionlogger actigraph is waterproof it can be attached with a one-time seal strap which cannot be removed without cutting.  This prevents a subject allowing someone ELSE to wear their actigraph!

Question: What do I do if I can’t get my Motionlogger to communicate and I’ve tried cleaning the pins with isopropyl alcohol and resetting in the interface?

Answer: When a fresh battery is put into a Motionlogger, there is a small chance that the unit’s microprocessor has been powered up in an unknown state.  This is why the instructions recommend “resetting” the actigraph in its interface whenever a fresh battery is inserted.  A properly reset actigraph should yield a double beep when the event button is pressed (more on this below).  But sometimes a simple reset is insufficient.  The following procedure will reestablish communications:

Question:  My Motionlogger communicates but I didn’t get a “double beep” reset signal from it after I changed the battery.

Answer: Sometimes if a battery (even a low one) is changed rapidly the internal capacitance of the actigraph is large enough to keep the actigraphs header and status in memory.  In this case the actigraph does not KNOW that its battery has been changed.  If one were to establish direct communications (steps 3 through 5 above) and enter CTRL-H on the keyboard, one would note that the header from the previous usage has remained.  Notations like “battery low” or “memory full” may also remain.  In fact, in some cases an actigraph may continue running through a battery change.  This is not detrimental to the actigraph.  The only issue which may be problematic is that the battery log does not reset to zero days of runtime.  This can be addressed in a number of ways.