Cortex is the data acquisition software most often used in this laboratory. Thalamus is an interface box that takes full advantage of all the Cortex features. The following description should be complete enough to allow reproduction of Thalamus. It should also provide sufficient information for those who wish to design their own interface for Cortex, including a much-simplified arrangement.
Click on the block diagram to see the key components of Thalamus. There are other circuits in Thalamus as well, including a 5 volt power supply (available externally) and touch-sensitive switch amplifiers. These are described in other diagrams.
The only essential circuitry for running Cortex is one spike latch for each spike (single-unit) input. Thalamus supports 8 spike latches. It also has an output to daisy-chair other spike latches. We have used 48 latches at a time, and hundreds are possible. Thalamus also has a pulse-generating circuit that is used to trigger a typical reward delivery device. Thalamus uses a single printed circuit card to provide both the latch and reward circuits. While this card is designed for use with the Thalamus, the printed circuit card is easily adapted for use in simpler systems. We highly recommend looking at the design of this card if you are considering building your own circuitry. We have an example circuit for using this card. Download the schematics here:
Spike Latch/Reward Pulse schematics
(Adobe Acrobat .pdf file)
Example circuit schematic
(Adobe Acrobat .pdf file)
One circuit that has found great utility in the laboratory is the Touch Pad Controller. This circuit uses minute currents to detect an animal's contact with isolated metal surfaces. It allows any metal surface to act like a push-button switch. The Touch Pad Controller can be wired into its own box, but we simply include it as part of the Thalamus. The design shown here can accommodate up to six contact surfaces by using six detector circuits. The animal is grounded either directly or via some resistance below 100K ohms. The "pad" inputs are connected to the contact surfaces. The output of each circuit is a 0 to 5v logic signal. These diagrams are of an older design. They work, but the newer circuits are less sensitive to static discharge and more sensitive to touch.
Touch Pad Controller, requires
six touch detector circuits (Adobe Acrobat .pdf file)
Touch detector circuit (Adobe
Acrobat .pdf file)
Here is another stand-alone circuit that has been integrated into the Thalamus. Anti-alias filters are essential if you want believable or publishable data. There are various solutions to filtering. We have chosen a flexible, albeit somewhat expensive approach. Thalamus uses four resistor programmable low-pass filter modules (Frequency Devices Model 746LT-3). These modules are now out of production, but Frequency Devices has similar ones available. The low-pass cutoff frequency is chosen using a resistor pack of six one-percent tolerance resistors soldered onto a DIP header. We have built these resistor packs to cover 50, 100, 200, 250, and 500 Hz. Any of the four analog channels can use any of these frequencies, but since the Cortex Program cannot digitize different channels at different speeds, we always set the four filters to the same cutoff frequency. We usually sample at 250 Hz and use a filter cutoff at 100 Hz. This guarantees the Nyquist criteria with an adequate guard band.
Anti-alias filter (Adobe Acrobat .pdf file)
[Home] [Section Info] [Computing] [LSN] [DIRP] [NIMH] [NIH]
Return to the Section on Neurophysiology Home Page
Send web site comments to the WEBMASTER.
last updated 29 December 2004