Cortical state refers to the dynamic patterns of activity in the brain, which influence how information is processed. This review discusses how cortical state is regulated in rodents and how attention modulates processing in primate visual cortex. Cortical states are characterized by fluctuations in low-frequency activity and spiking correlations, and are mediated by common receptor systems. Attention is thought to involve processes similar to state changes, operating at a local level to enhance the representation of salient features while suppressing internally generated activity. Cortical activity in primary sensory areas is not strictly determined by sensory input but reflects an interaction between external stimuli and spontaneous patterns. Cortical states are not strictly synchronized or desynchronized but form a continuum of states. During sleep, cortical activity is more synchronized, while during waking and REM sleep, it is more desynchronized. However, within wakefulness, cortical states also vary, with awake quiescent animals showing spontaneous fluctuations similar to those during slow-wave sleep. Attention enhances the detection of certain stimuli by increasing spiking responses and reducing low-frequency fluctuations, trial-to-trial variability, and correlations. These effects resemble cortical desynchronization, occurring specifically in parts of cortex that represent the attended stimulus. Attention involves similar processes to those causing cortical desynchronization, but operating at a local level. This local desynchronization arises from a combination of diffuse neuromodulatory inputs and tonic glutamatergic drive focused on the cortical populations representing the attended stimulus. Cortical state is influenced by various factors, including neuromodulatory and glutamatergic inputs. The cholinergic system plays an important role in controlling cortical state, with increased activity leading to desynchronization. However, cholinergic input is not necessary for cortical desynchronization, as some animals show atropine-resistant desynchronization. Other neuromodulatory systems, such as serotonin and norepinephrine, also contribute to cortical desynchronization. Cortical state and sensory responses are closely related. Cortical state influences how sensory stimuli are processed, with punctuate stimuli generating large responses in both synchronized and desynchronized states, while temporally extended stimuli are better represented in desynchronized states. Attention modulates these responses, reducing variability and increasing the representation of repeated or extended stimuli. The mechanisms underlying attention and cortical state are complex, involving interactions between various neuromodulatory and glutamatergic systems. Recent studies suggest that these mechanisms are similar in both rodents and primates, with attention affecting cortical state at a local level. Future research using modern techniques such as optogenetics and enzyme-linked electrochemistry may help to further elucidate the role of different neuromodulatory systems in shaping cortical state and information processing.Cortical state refers to the dynamic patterns of activity in the brain, which influence how information is processed. This review discusses how cortical state is regulated in rodents and how attention modulates processing in primate visual cortex. Cortical states are characterized by fluctuations in low-frequency activity and spiking correlations, and are mediated by common receptor systems. Attention is thought to involve processes similar to state changes, operating at a local level to enhance the representation of salient features while suppressing internally generated activity. Cortical activity in primary sensory areas is not strictly determined by sensory input but reflects an interaction between external stimuli and spontaneous patterns. Cortical states are not strictly synchronized or desynchronized but form a continuum of states. During sleep, cortical activity is more synchronized, while during waking and REM sleep, it is more desynchronized. However, within wakefulness, cortical states also vary, with awake quiescent animals showing spontaneous fluctuations similar to those during slow-wave sleep. Attention enhances the detection of certain stimuli by increasing spiking responses and reducing low-frequency fluctuations, trial-to-trial variability, and correlations. These effects resemble cortical desynchronization, occurring specifically in parts of cortex that represent the attended stimulus. Attention involves similar processes to those causing cortical desynchronization, but operating at a local level. This local desynchronization arises from a combination of diffuse neuromodulatory inputs and tonic glutamatergic drive focused on the cortical populations representing the attended stimulus. Cortical state is influenced by various factors, including neuromodulatory and glutamatergic inputs. The cholinergic system plays an important role in controlling cortical state, with increased activity leading to desynchronization. However, cholinergic input is not necessary for cortical desynchronization, as some animals show atropine-resistant desynchronization. Other neuromodulatory systems, such as serotonin and norepinephrine, also contribute to cortical desynchronization. Cortical state and sensory responses are closely related. Cortical state influences how sensory stimuli are processed, with punctuate stimuli generating large responses in both synchronized and desynchronized states, while temporally extended stimuli are better represented in desynchronized states. Attention modulates these responses, reducing variability and increasing the representation of repeated or extended stimuli. The mechanisms underlying attention and cortical state are complex, involving interactions between various neuromodulatory and glutamatergic systems. Recent studies suggest that these mechanisms are similar in both rodents and primates, with attention affecting cortical state at a local level. Future research using modern techniques such as optogenetics and enzyme-linked electrochemistry may help to further elucidate the role of different neuromodulatory systems in shaping cortical state and information processing.