LFP Assignment Papers

Question 1

The current sources and sinks generating the LFP have been well-studied in vitro and under anesthesia; nonetheless, there remain open questions regarding the usefulness of the LFP for inferring synaptic activity of individual neurons in intact, awake cortex.

What are these three question concerning?

Answer 1

1. One open question concerns the relationship of the LFP to
   intrinsic, nonsynaptic currents in single neurons.
2. A second question concerns the relative roles of synaptic excitation and inhibition.
3. A third question concerns the effect of sensory stimuli on the relationship between the LFP and synaptic currents.

Question 2

Why is there an open question concerning the relationship between LFPs and intrinsic, non-synaptic currents in single neurons?

Answer 2

Studies in vitro indicate that intrinsic currents provide a measurable contribution to the LFP in both hippocampus and neocortex. Large-scale simulations have offered differing estimates of this contribution: some suggest that the LFP mainly reflects synaptic activity, and others suggest a dominant role for intrinsic conductances. It is not known how the LFP relates to subthreshold activity in single neurons, particularly in the intact and awake cortex.

Question 3

Why is there an open question concerning the relative roles of synaptic excitation and inhibition?

Answer 3

The traditional view is that the cortical LFP largely reflects the activity of pyramidal neurons, which are numerous and well-aligned in space. Indeed, activation of excitatory afferents produces large and localised extracellular current sinks. Inhibition, conversely, is thought to contribute little to the cortical LFP because inhibitory cells and synapses are fewer, have lower driving force, and are not well-aligned in space. However, measurements in vitro have revealed conditions where the LFP reflects inhibitory activity, both in hippocampus and in neocortex. Moreover, inhibitory currents recorded in vitro and under anesthesia are involved in fast patterns in the LFP. It remains unknown how the LFP is related to synaptic excitation and inhibition of individual neurons in the intact, awake cortex.

Question 4

Why is there an open question concerning why there is an open question concerning

Answer 4

Extracellular recordings show that visual stimulation reduces the correlation between spikes and the LFP in mouse primary visual cortex (V1), both under anesthesia and in
wakefulness. Synaptic mechanisms underlying these changes in the relationship between the LFP and single neurons remain unclear.

Question 5

What are meant by intrinsic conductances?

Answer 5

Conductances sub-threshold to action potentials