Neuropsychology Psychology 162, Fall 2008

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Determining the Receptive Field Laboratory: Week 2

Description of the Laboratory

This is a continuation of the lab you did last week.  Much of it is a repeat, but there are more than simple cells to be found in your recordings so you will have to be more careful in how you stimulate your cell.

Goals for the Laboratory

1. To develop further  your skills in systematic observation, the hallmark of science
2. To develop further your skills in making conclusions from data, a fundamental skill in science
3. To develop skills in communicating your findings and conclusions
4. To understand more fully one method of understanding the brain, single cell recording.

Directions for the Laboratory

Before beginning the laboratory, download and copy the spreadsheet that has been developed for data collection.  It will  help guide you in your attempts to determine the optimal stimulus for the cells that you are recording from.  Bring a copy on a thumb drive to class or use your vault account.

Then open the activity from the link at the bottom of the page.  You will be presented with a full screen to run the simulation.  The screen is structured as seen below and is identical to the last lab:

On the far left is the menu that will allow you to pick a stimulus to use to stimulate your cell.  The choice are a black field (default), a white field, a white dot, a white bar, a black bar, and a moving bar (white).  The center of the screen is the area of the retina that you can stimulate.  To simplify matters, it is also the receptive field.  For this lab, you do not need to hut for the receptive field. 

Around and below the receptive field are controls for the stimulus.  The sliders to the right and immediately below the receptive field control the position of the stimulus.  You can also move the stimulus by clicking or dragging your mouse over the receptive field.  You can adjust the width of the bar and the diameter of the dot using the Stimulus Size slider.  For the bar stimuli, you can control the tilt or orientation using the Stimulus Orientation slider.   Finally, for ease, you can center your stimulus in the receptive field by simply clicking the Center Stimulus button.  One additional feature that will be more important in this lab.  When the stimulus is a moving bar, a new button is added right next to the Center Stimulus button.  This button is labeled Reverse Direction and it allows you to have the moving bar move in the exact opposite direction.

Below the stimulus controls is the button you need to press to get a new cell to examine.

The right side of the screen has a graph of the cells firing rate.  The height of the bar indicates the number of action potentials a second.  The current value is plotted as part of the x-axis legend.  Also, to smooth out the values, the average of the last 10 readings is printed out as well.

This screen is your experimental world for this experiment.  Your goal is to try and determine the optimal stimulus for 15 different cells.  Your lab partner will do the same giving you 30 cells together to have to characterize.  However, in the last lab, there was only one cell type, the cell type that Hubel and Wiesel called Simple Cells.  In this lab, there are more than one type of cell.  Your task is to determine the two general cell types and to determine the differences in how these two cells respond to stimuli.

The spreadsheet that you downloaded has been developed to help guide you through this process.  However, do not let it limit you.  Use it as a starting point.  A sample spreadsheet is shown below (Given space, some of the labels might be a bit different in the actual excel sheet).

The cell simply indicates which cell the data belongs to.  The number is to indicate the order you recorded from the cell.  The next four columns are to indicate firing rate to some basic stimuli: a complete black screen, a completely filled white screen, a small dot (choose a small size) in the center of the receptive field, and a small dot outside the center.  The next column are where you indicate whether the cell responds to a white or dark bar in the center better, if it is a simple cell.  The other cell type does not prefer white over black bars so check carefully here.  The next two columns is where, after determining the optimal bar orientation and width, what is the firing rate for the bar in the center of the receptive field versus the surround area of the receptive field.  The next column, indicate the preferred orientation of the stimulus.  Next, indicate the width of the preferred stimulus.  The second to last column is particularly related to using moving bar stimuli.  Basically, you want to test a bar of the optimal orientation and width and see how it responds as it moves through the receptive field in both the default direction and the opposite direction.  Is there a difference in the cells response to the two directions?  If so, then the cell prefers 1 motion direction and put a 1 in this column.  If the response is the same to the two directions, put a 2 in the column.  The final column you indicate the firing rate of the preferred stimulus.  For the simple cells, this should match the firing rate for the optimal bar in the center of the receptive field.  Let me reiterate.  This is a minimal summary chart.  There is much else to learn here.

Issues to consider:

• What is the best way to distinguish the two cell types?
• What seems to be the role of the two cell types?  What I mean is what do the two cells seem to be most selective about?  What most affects their firing rate?
• Is orientation and width important to both types of cells?
• How does the two cells respond to a moving stimulus?

Laboratory Write-up

You now have two sets of data.  Treat the first set separately in your lab report but you may combine all of the information for the section of the report that belongs to this part of the report.

So in this report, you need to take the 30 cells that you and your partner have and describe what you think you have found.  Again, you will write a results and discussion section and one group will present their results from this section of the lab to the class.

Results

Again, look at all your data and think about what you have found.  In addition, to the questions above, some questions you might want to consider are:

• Are there more of one cell type or the other?
• How do the preferred orientations and widths compare between the two cell types?
• Which cell type is more common?

Remember, you are trying to generalize from your sample to what you think all the cells in this area of the brain are responding to.

You have the same task, but a more complex version of the task, as for the last part of the lab.

Discussion

Same issues as last lab. 

We will discuss this more in class.

Links to lab simulation and spreadsheet

Click here to open the laboratory simulation.

Click here to get the sample spreadsheet for data collection.

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