Biomedical subjects

Chris van der Togt

Publications and source records attributed to Chris van der Togt.

4 recordsLinked to original sources

PubMed2005

Synchrony dynamics in monkey V1 predict success in visual detection.

Behavioral measures such as expectancy and attention have been associated with the strength of synchronous neural activity. On this basis, it is hypothesized that synchronous activity affects our ability to detect and recognize visual objects. To investigate the role of synchronous activity in visual perception, we studied the magnitude and precision of correlated activity, before and after stimulus presentation within the visual cortex (V1), in relation to a monkey's performance in a figure-ground discrimination task. We show that during the period of stimulus presentation a transition in synchronized activity occurs that is characterized by a reduction of the correlation peak height and width. Before stimulus onset, broad peak correlations are observed that change towards thin peak correlations after stimulus onset, due to a specific decrease of low-frequency components. The magnitude of the transition in correlated activity is larger, i.e. a stronger desynchronization occurs, when the animal perceives the stimulus correctly than when the animal fails to detect the stimulus. These results therefore show that a transition in synchronous firing is important for the detection of sensory stimuli. We hypothesize that the transition in synchrony reflects a change from loose and global neuronal interactions towards a finer temporal and spatial scale of neuronal interactions, and that such a change in neuronal interactions is required for figure-ground discrimination.

Animals↗

PubMed2005

Neural responses in cat visual cortex reflect state changes in correlated activity.

Cortical state is characterized by ongoing rhythmic neural activity. Changes in rhythmic activity and thus in cortical state are shown to occur spontaneously in the anesthetized cat. We were interested in whether these state changes have an affect on the cortical processing of sensory stimuli. This was investigated by recording spontaneous and stimulus-evoked local field potentials and multi-unit neuronal activity (MUA) from trans-cortical electrode arrays in the visual cortex of the anesthetized cat. Changes in cortical state were identified by calculating the cross-correlation strength and cross-coherency, between MUA channels at different layers and on separate electrode arrays. Spontaneous changes in rhythmic activity were associated with changes in the strength of stimulus-evoked multiple unit responses of cortical neurons. The highest multi-unit responses were found in periods when low-frequency rhythms of the electroencephalogram increase in magnitude and high-frequency rhythms decrease. Such changes in evoked responses were maximal at layer IV, the input layer of the visual cortex. Our findings suggest that stimulus response magnitude depends on rhythmic state and reflects changes in functional connectivity within the visual cortex.

Action Potentials↗

PubMed2004

Correspondence of presaccadic activity in the monkey primary visual cortex with saccadic eye movements.

We continuously scan the visual world via rapid or saccadic eye movements. Such eye movements are guided by visual information, and thus the oculomotor structures that determine when and where to look need visual information to control the eye movements. To know whether visual areas contain activity that may contribute to the control of eye movements, we recorded neural responses in the visual cortex of monkeys engaged in a delayed figure-ground detection task and analyzed the activity during the period of oculomotor preparation. We show that approximately 100 ms before the onset of visually and memory-guided saccades neural activity in V1 becomes stronger where the strongest presaccadic responses are found at the location of the saccade target. In addition, in memory-guided saccades the strength of presaccadic activity shows a correlation with the onset of the saccade. These findings indicate that the primary visual cortex contains saccade-related responses and participates in visually guided oculomotor behavior.

Animals↗

PubMed2003

Internal state of monkey primary visual cortex (V1) predicts figure-ground perception.

When stimulus information enters the visual cortex, it is rapidly processed for identification. However, sometimes the processing of the stimulus is inadequate and the subject fails to notice the stimulus. Human psychophysical studies show that this occurs during states of inattention or absent-mindedness. At a neurophysiological level, it remains unclear what these states are. To study the role of cortical state in perception, we analyzed neural activity in the monkey primary visual cortex before the appearance of a stimulus. We show that, before the appearance of a reported stimulus, neural activity was stronger and more correlated than for a not-reported stimulus. This indicates that the strength of neural activity and the functional connectivity between neurons in the primary visual cortex participate in the perceptual processing of stimulus information. Thus, to detect a stimulus, the visual cortex needs to be in an appropriate state.

Animals↗