single unit electrophysiology

single unit electrophysiology learning goals: •

understanding of the method of electro-physiological recording from single cells

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understanding of the concept of “receptive fields”

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basic idea of ways of interpreting the activity of single cells with regard to cognition

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scope and limits of this method possible questions to ask etc.

activities: •

reading

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watching videos showing research

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interactive applet: mapping receptive fields

Introduction One widely used method of investigating the workings of the nervous system is inserting electrodes into the brain and trying to record electrophysiological activity of single neurons. So how do you “query” single neurons (out of the 100 billions “living” in the brain...), what is measured/recorded and in how far does this help us to understand the workings of the nervous system, “information processing”, or cognition? In order to explore those questions and get a basic understanding of the method, this sample focuses on classic work on the visual system (retina, thalamus, and visual cortex, part 1) and more current work on “higher” visual functions, multimodal integration, and the interplay of action and vision (part 2). Part 1 focuses on experiments done by Steven Kuffler, David Hubel, and Torsten Wiesel, which were performed on anesthetized cats. This work contributed much to the understanding of the visual system and resulted in a Nobel Prize. They were recording from neurons at different “stages” of visual processing: from ganglion cells of the retina (Kuffler 50ies), cells of the LGN (Lateral Geniculate Nucleus) of the thalamus and from primary visual cortex (Hubel, Wiesel) analyzing their respective “receptive fields”. Part 2 introduces examples from current research giving an outlook on yet more complex issues such as: a) object perception – introducing the work of Keiji Tanaka et al., Charles Gross, David Perrett et al b) integration of different modalities – as studied by Michael Graziano's group. Rossmanith, Reichelt 2010

physiology sample #3: single unit electrophysiology

c) perception and action – focusing on work on mirror neurons done by the Parma group (Rizzolatti, Fogassi, Gallese, et al.). Mirror neurons also share multi-modal properties and are connected to the neurons in the temporal sulcus studied by Perrett et al. Inserting electrodes into the brain is an invasive procedure and therefore these experiments were done on laboratory animals – with obvious ethical implications... The visual cortex in a monkey, stained by the Golgi method, shows a few pyramidal cells — a tiny fraction of the total number in such a section. The entire height of thephotograph represents about 1 millimeter. A tungsten microelectrode, typical of what is used for extracellular recordings, has been superimposed, to the same scale. Eye, Brain, and Vision

Suggested session organization Work through part 1 and then choose one or more examples from part 2 according to interest and the amount of time remaining. Reserve 20 to 30 minutes for reflection and discussion (questions to explore). Part 1: Understanding the visual system by mapping receptive fields (Kuffler, Hubel, Wiesel) Understanding the basics of electrophysiological recordings from single cells by looking at classical research 1) Read the 2+ pages “background” text from the Insight Applet, which gives information about the method of electrophysiological recording of single nerve cells and especially about the concept of “receptive fields” and check out the illustrations from Kandel's principles (see the pdf linked on the website). You may want to look at how electrodes are made 2) Have a look at the animation from sumanasinc about receptive fields in the retina (ca. 10') 3) Explore the research practice of Hubel & Wiesel by reading an excerpt of Eye, Brain and Vision and watching the video (16') showing how they record from LGN and primary visual cortex 4) Explore receptive field mapping – interactive applet from Insight Try-out for yourself what looks so easy and straightforward in the video: ✔

Goldstein’s Sensation & Perception Lab, → “Insight” → “demonstration” → “receptive field mapping”

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read “instructions” first,

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go on to mapping retinal ganglion cells, lateral geniculate cells (thalamus), and primary visual cortex cells

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in each window 2 receptive fields are to be mapped

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mapping probably needs some practice → you can try/repeat several times: by pressing reset: 2 new receptive fields are presented

Rossmanith, Reichelt 2010


Part 2: an outlook at more complex issues - 3 examples of current research The concept of a receptive field has been immensely productive in neuroscience, yet recent research takes this concepts to whole new levels. Explore some of the lines of research which extend the concept to more complex forms (a), interactions with other sensory modalities and action (b), and even other persons (c). You will probably have little time remaining to delve into these subjects, so get a brief overview and decide what issues interest you the most. Keep in mind the notion of “receptive field” and consider if or in how far it still applies... a) complex forms and objects ✗ ✗

Goldstein Sensation & Perception 118-122 further reading: Cadieu, C., M. Kouh, A. Pasupathy, C. Connor, M. Riesenhuber, and T. Poggio. A Model of V4 Shape Selectivity and Invariance, Journal of Neurophysiology, Vol. 98, 1733-1750, June, 2007.

b) across senses/modalities & combining perception and action ✗

Goldstein Sensation & Perception 118-122

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Graziano, M. S., Gross, C. G., Taylor, C. S. and Moore, T. (2004). A system of multimodal areas in the primate brain. in: Crossmodal Space and Crossmodal Attention. C. Spence and J. Driver (eds.). Oxford: Oxford University Press: 51-67.

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Maravita, A. & Iriki, A. (2004). Tools for the body (schema). Trends in Cognitive Sciences 8(2): 79-86. (first section: Neurophysiology of tool-use in macaque monkeys: p1-3)

c) mirror neurons ✗

Depth electrode recording in the human brain: Evidence for pervasive mirroring a talk by Marco Iacoboni (first 10-15 minutes) includes original video sequences of the mirror neuron experiments performed in the Rizzolatti lab

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Rizzolatti, G., Fogassi, L. and Gallese, V. (2006). Mirrors in the mind. Scientific American 295(5): 54-61.



Selected material for further exploration retina: Lettvin, J. Y., Maturana, H. R., McCulloch, W. S. and Pitts, W. H. (1959). What the Frog's Eye Tells the Frog's Brain. Proceedings of the Institute of Radio Engineering 47(11): 1940-51. WebVision Kolb, H. (2003). How the retina works. American Scientist, 91(1), 28–35.

visual cortex Eye, Brain, and Vision (a classic now as online book,) Hubel, David H. (1981). http://nobelprize.org/nobel_prizes/medicine/laureates/1981/hubel-lecture.pdf. Nobel lecture.



Questions to explore Shortly describe the method: ✗

What is done and what is recorded?

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What is a “receptive field?”

Please draw one or more (perhaps different views are needed) sketches of the brain and approximately mark the regions where the respective kinds of neurons investigated in the examples are located respectively and what kind of stimuli they are sensitive to. Give a short description of the properties of the neurons investigated in the examples ✗

How does firing change in relation to specific stimuli?

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What does this tell us about the concept of neuronal coding, about the process of information processing, and about perception?

Compare the different examples ✗

How do the stimuli differ, how do the firing properties of the neurons differ?

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For example, research on mirror neurons has been criticized for not adequately controlling the experimental situations, i.e. the stimuli used. Is this critique valid? How do the stimuli used to study mirror neurons differ from, for example, the stimuli used in research on the visual system in the occipital lobe? What are the respective advantages, disadvantages of using such stimuli?

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Can you think of other examples where single cell recording contributed to the understanding of “information processing” in the brain/cognition?

General questions: ✗

What can be learned about cognition by recording from single neurons?

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Is this method suitable to investigate cognition? Why / why not?

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What aspects of cognition can be investigated?

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What kind of question can we ask? - Give some examples

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What kind of answers do we get?

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What are the strengths and what are the limits of this method?

