Thalamocortical, not Intracortical, Inputs Set the Wakeful Activity Levels of Cortical Visual Inhibition
Cortical neurons integrate from a wide range of synaptic inputs, locally within the cortex and distally from multiple brain sources, which altogether support the generation and transmission of spikes. Yet, the relative influence on local cortical processing between thalamocortical and intracortical inputs still remains poorly understood. Here, we used tangential insertion of high-density silicon…
The study utilized high-density silicon probes to investigate the functional connections between thalamocortical and intracortical pathways. By analyzing cortical activity during wakefulness and light anesthesia, researchers observed a significant increase in firing rates for thalamocortical axons and cortical inhibitory neurons. This increase was uniform across both neuron populations, whereas neighboring excitatory neurons showed minimal change.
The researchers determined that thalamocortical axons preferentially connect to cortical inhibitory neurons, with a 90/10% ratio. Moreover, they discovered that wakefulness-induced activity changes are symmetrical in thalamocortical synapses but asymmetrical in intracortical synapses. Within intracortical synapses, firing rates primarily rise in receiving neurons, while pre-synaptic neurons remain largely unaffected.
Conversely, thalamocortical receiving excitatory neurons experience a notable increase in firing during wakefulness, unlike the majority of the cortical excitatory population.
Through mathematical modeling of spike transmission in both thalamocortical and intracortical networks, the study concluded that the observed homogeneous wakeful increases in thalamocortical and cortical inhibitory neurons could only be replicated if thalamocortical inputs outnumbered intracortical inputs. Ultimately, the findings highlight thalamocortical synaptic inputs as a crucial factor in determining the wakeful firing levels of inhibitory neurons in the initial stage of visual cortical processing.
Written by urgent.news from bioRxiv's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
