Abstract
The cortex modulates activity in superior colliculus via a direct projection. What is largely unknown is whether (and if so how) the superior colliculus modulates activity in the cortex. Here, we investigate this issue and show that optogenetic activation of superior colliculus changes the input–output relationship of neurons in somatosensory cortex, enhancing responses to low amplitude whisker deflections. While there is no direct pathway from superior colliculus to somatosensory cortex, we found that activation of superior colliculus drives spiking in the posterior medial (POm) nucleus of the thalamus via a powerful monosynaptic pathway. Furthermore, POm neurons receiving input from superior colliculus provide monosynaptic excitatory input to somatosensory cortex. Silencing POm abolished the capacity of superior colliculus to modulate cortical whisker responses. Our findings indicate that the superior colliculus, which plays a key role in attention, modulates sensory processing in somatosensory cortex via a powerful di-synaptic pathway through the thalamus.
Highlights
The cortex modulates activity in superior colliculus via a direct projection
Work in monkeys indicates that superior colliculus (SC) can modulate activity in higher order cortical areas, with visual responses in the middle temporal area (MT) of monkeys disappearing when lesions of primary visual cortex are combined with lesions of SC10
Receiver operating characteristic (ROC) analysis indicated that the vast majority of neurons in SC (91%; 50 out of 55; p < 0.05 ROC bootstrap analysis) significantly increased their action potential firing in response to brief (15 ms) optogenetic activation (Fig. 1c–e; Supplementary Fig. 1a–c)
Summary
The cortex modulates activity in superior colliculus via a direct projection. What is largely unknown is whether (and if so how) the superior colliculus modulates activity in the cortex. Our findings indicate that the superior colliculus, which plays a key role in attention, modulates sensory processing in somatosensory cortex via a powerful di-synaptic pathway through the thalamus. Similar to these earlier studies in primates and cats, more recent work in mice indicates that SC modulates visual responses in higher order cortical visual areas[15] as well as in the postrhinal cortex[16]. It has recently been shown that SC can modulate responses in primary visual cortex in mice, through the dorsolateral geniculate nucleus rather than the pulvinar[17] Together, these studies allude to the importance of the SC for visual processing in both primary and higher order visual areas in the cortex.
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