Question

6. A. One hundred pyramidal cells in a cortical gyrus receive an excitatory input at their distal dendrites, resulting in transiently synchronous excitatory postsynaptic potentials (EPSPs). Draw the signal you would expect to record from an electrode placed on the surface of the scalp, and indicate the direction (up or down) that corresponds to positive and negative voltage (4 points): B. The same one hundred pyramidal cells receive an excitatory input close to their cell bodies, resulting again in synchronous EPSPs. Draw the signal you would expect to record from an electrode placed on the surface of the scalp, and indicate the direction (up or down) that corresponds to positive and negative voltage (4 points): 7. The EEG is thought to be preferentially sensitive to current flow along cortical pyramidal neurons. A. Explain why the EEG is thought to be more sensitive to current flow along pyramidal cells than to current flow along other cell types in the cortex (2 points). B. Provide one reason why the EEG is thought to be more sensitive to current flow along cortical neurons than to current flow along neurons in subcortical brain regions (e.g. hippocampus) (2 points). 8. You observe an increase in the amplitude of an oscillation in the EEG signal. A. List two possible changes in network activity that could result in the observed increase in amplitude (4 points).

Answer 1

6. for this A and B refer to attached picture

initiation of dendritic action potentials19,20. These local spikes did not propagate as action potentials to the soma; instead, larg. er, more rapidly rising EPSPs were observed in the soma follow ing dendritic spikes. Because local spiking usually occurred only on the third or fourth stimulus of a train, summation occurring at the soma was elevated (Fig. 3b and c). Thus there was very lit- tle dependence of temporal summation on EPSP amplitude with- out local initiation of dendritic action potentials. Furthermore, local spiking seems to provide the neuron with a mechanism to overcome the spatial normalization of temporal summation. a Dendritic / injections dend AP no AP Dendrite Dendrite Summation (% increase) AZD7288 control dend AP no AP 25 mV 10 mV 25 ms 50 ms Soma 2 4 6 8 d-AP First EPSP (mV)

7.

     A)  Pyramidal neurons of the cortex are thought to produce the most EEG signal because they are well-aligned and fire together. Because voltage field gradients fall off with the square of distance, activity from deep sources is more difficult to detect than currents near the skull

    B) Neurons in the human cortex generally process their information by means of electrical signals and thus enable the electrical recording of their activity, the electroencephalogram (EEG). Due to their unique orientation with their long apical dendrites perpendicular to the cortical surface, large cortical pyramidal neurons in deep cortical layers play a major role in the generation of the EEG. Specific and non-specific thalamic nuclei, as well as distant cortical areas, terminate on these apical dendrites and form myriads of excitatory and inhibitory afferents. The release of excitatory and inhibitory neurotransmitters by these fibers activates specific postsynaptic receptors and generates excitatory and inhibitory postsynaptic potentials, respectively. By electrotonic spread of postsynaptic potentials along the apical dendrites and equivalent capacitive currents, they become electrical dipoles. Positive or negative deflections are generated by both excitatory and inhibitory afferents, depending on the location of these synapses on the apical dendrites. Negative (upward) deflections are due to superficial excitatory or deep inhibitory inputs, whereas positive (downward) deflections represent deep excitatory or superficial inhibitory inputs.

8.

A) Hypersynchrony, photic stimulation and sleep depriviation is the reason for increase in amplitude of EEG signals.