Synaptic interactions between thalamic and cortical inputs onto cortical neurons in vivo

Area of Science:

• Neuroscience
• Computational Neuroscience
• Systems Neuroscience

Background:

• Understanding thalamocortical and corticocortical interactions is crucial for deciphering brain function.
• Neocortical neurons receive convergent input from both the thalamus and other cortical areas.
• The precise nature of these interactions, particularly inhibitory mechanisms, remains an active area of research.

Purpose of the Study:

• To investigate the synaptic interactions between thalamic and cortical inputs onto neocortical neurons.
• To characterize the effects of paired-pulse stimulation (PPS) on homosynaptic and heterosynaptic inputs.
• To elucidate the underlying mechanisms, such as shunting inhibition, responsible for observed synaptic interactions.

Main Methods:

• Intracellular recordings were performed on anesthetized cat cortical and thalamocortical neurons.
• Paired-pulse stimulation (PPS) was applied to homosynaptic (cortico-cortical, thalamocortical) and heterosynaptic (thalamocortical and corticocortical) pathways.
• Changes in excitatory postsynaptic potentials (EPSPs) and apparent input resistance (R(in)) were measured at various time intervals.

Main Results:

• Cortico-cortical pathways exhibited facilitation, depression, or no significant effect.
• Cortical responses to thalamocortical inputs were predominantly facilitated.
• Heterosynaptic interactions generally decreased EPSP amplitudes and areas, primarily through shunting inhibition, with maximal effects around 10 ms.

Conclusions:

• Thalamocortical and cortical inputs onto cortical neurons engage in strong, short-lasting shunting inhibition.
• Shunting inhibition, indicated by decreased input resistance, significantly reduces synaptic responsiveness.
• These findings highlight a critical inhibitory mechanism shaping information processing in the neocortex.