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October Tech Tip -
Channel Cloning
One of the limitations of
using analog filtering of signals, is that they
are physically changed prior to digitization. In
order to use different filters on the same signal
you
need to split the signal before it gets
to the analog filtering stage, and then run
it through two different analog filters. This limitation applies
to all analog filtering, including our own
Lynx-8 based systems. If you are using all of
the inputs to all of your Lynx-8's, there is no
way to filter a signal two different ways without
sacrificing a channel you are already
using.
Digital systems, such as the
Digital Lynx, eliminate the channel duplication
problem by digitizing and sending the signal to
Cheetah without any analog domain modification.
This allows Cheetah to perform digital filtering
(referred to as Digital Signal Processing or DSP)
on
the signal. Because of this,
you can actually make unlimited copies, known
as "clones," of each input channel
and use Cheetah to perform the filtering. Changes
to the settings of an
acquisition entity using one of the cloned channels
will not affect any other acquisition entities using
other clones of that channel.
The most common use
of channel cloning is to record a continuous version
of one of the channels of a
Tetrode. Doing this allows you to filter for
low frequency signals, such as theta,
while still recording the high frequency
spike activity without any special connections or equipment. The rest
of this Tech Tip will explain how to
setup these cloned channels using
Cheetah.
To keep things simple, we'll
use a Cheetah setup with only two Tetrodes. To do
this, use Notepad to edit the Cheetah.cfg
file in Cheetah's Configuration directory and find
the ELECTRODE CONFIGURATIONS section of
the file. Ensure that the only line in that
section that does not start with the "#" sign is
the one saying -ProcessConfigurationFile
2tt.cfg
.
Save the changes to the
Cheetah.cfg and close Notepad. You can
then start Cheetah and click the button that says
"Start Cheetah Using the Following File" to use
the changes we made to the Cheetah.cfg.
After Cheetah starts, you will see a single
spike window showing both of our Tetrodes.
Now we
need to create a CSC for the first
subchannel of each Tetrode using cloned channels. We'll
create a new configuration file by opening up
Notepad. The first thing we need to do is
to create a CSC acquisition entity using the
following command:
-CreateCscAcqEnt TT1_CSC
AcqSystem1
Next we need to tell Cheetah
what AD Channel we want
to use for this new CSC. In this
case, we want the first subchannel of TT1, which happens to
be AD Channel
0:
-SetChannelNumber TT1_CSC
0
The
-SetChannelNumber
command is what
creates a clone of AD Channel 0. For the second
CSC, we just need to use the same two commands,
changing the names and channel numbers to appropriate values. The
final file should look like
this:
-CreateCscAcqEnt TT1_CSC
AcqSystem1
-SetChannelNumber TT1_CSC
0
-CreateCscAcqEnt TT2_CSC
AcqSystem1
-SetChannelNumber TT2_CSC
4
Save the
file as 2TT_ClonedCSC.cfg.
Back in
Cheetah, go to the File menu and select Open
Configuration File. Find the
2TT_ClonedCSC.cfg file we just saved and
open it. Although nothing seems to have happened,
we just created the acquisition entities for the
cloned CSC's. Even though the CSC's aren't
visible, you can adjust the acquisition entity
settings (e.g. filters, input range, sampling
rate, etc.), record the signal and stream it over
NetCom without affecting the signals of either of
the Tetrodes.
In order to
see the CSC Channels we just created, we need to
create a time window. Go to the Window
menu and select Add Window->Time
Window. Now select Add Plot(s) under
the Display menu item of the window we
just created. Click on TT1 in the AE
list, hold down the Shift Key and click the last
item in the list. It should be highlighted as
shown below:
Now click on
Add Acquisition Entities. Both the spikes
extracted from the Tetrodes as well as a
continuous version of the first subchannel of each
Tetrode are now visible in the time
window.
To create a saved configuration file, select Save
Cheetah Settings under Cheetah's
File menu. When Cheetah is started
again, use the Select a Different Startup
File option from Cheetah's configuration
selection window. Locate the saved file and
Cheetah will start with the saved settings,
including the cloned channels and
displays.
The above example shows manual configuration file loading and interactive
time window creation. This setup can also be accomplished by directly editing the
original electrode configuration file. For an example of
this setup in a Electrode .cfg file, click here
.
Cloning
channels is a very simple, yet powerful way to
change how you visualize and analyze the data
gathered from your experiments. Cloned channels do
not count toward your licensed channel limit, so
even if you have maxed out a 16 physical channel
license with four Tetrodes, you'll still be able
to create as many CSC's as you want using cloned
channels. This is the type of flexibility we are
constantly trying to provide as we introduce new
products. If you have any comments or suggestions
on how we can improve channel cloning or any other
ideas, please don't hesitate to let us
know. | 
