Transient Cortical Excitation at the Onset of Visual Fixation

Cognitive Neuroscience and Schizophrenia Program, Nathan S. Kline Institute for Psychiatric Research, Orangeburg, NY 10962, USA.
Cerebral Cortex (Impact Factor: 8.67). 02/2008; 18(1):200-9. DOI: 10.1093/cercor/bhm046
Source: PubMed

ABSTRACT Primates actively examine the visual world by rapidly shifting gaze (fixation) over the elements in a scene. Despite this fact, we typically study vision by presenting stimuli with gaze held constant. To better understand the dynamics of natural vision, we examined how the onset of visual fixation affects ongoing neuronal activity in the absence of visual stimulation. We used multiunit activity and current source density measurements to index neuronal firing patterns and underlying synaptic processes in macaque V1. Initial averaging of neural activity synchronized to the onset of fixation suggested that a brief period of cortical excitation follows each fixation. Subsequent single-trial analyses revealed that 1) neuronal oscillation phase transits from random to a highly organized state just after the fixation onset, 2) this phase concentration is accompanied by increased spectral power in several frequency bands, and 3) visual response amplitude is enhanced at the specific oscillatory phase associated with fixation. We hypothesize that nonvisual inputs are used by the brain to increase cortical excitability at fixation onset, thus "priming" the system for new visual inputs generated at fixation. Despite remaining mechanistic questions, it appears that analysis of fixation-related responses may be useful in studying natural vision.

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Available from: Peter Lakatos, May 23, 2014
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    • "The anatomical origins of the motor-related phase-resetting cues are uncertain, but plausible candidates are efference copies from the oculomotor system (pontine reticular formation and/or extraocular muscles, see Ito et al., 2011) or a corollary discharge route through the superior colliculus (SC), thalamus, and frontal eye fields (FEFs) (see Melloni et al., 2009). It is also possible that saccades and the corollary activity are both generated in parallel by attention (Melloni et al., 2009; Rajkai et al., 2008). (B) Selective attention orchestrates phase resetting of oscillations in auditory and visual cortices (e.g., Lakatos et al., 2008). "
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    • "This synchronization in the local field potential signal is thought to be of non-retinal origin since it is observed in visual areas, even in the dark, during voluntary eye-movements. Similar processes could apply also to micro-fixation movements (Maldonado et al., 2008; Rajkai et al., 2008; Bosman et al., 2009). Recent work (Martinez-Conde et al., 2012) indicates that real micro-saccadic eye-movements during visual fixation trigger a phasic increase in firing rate, followed by a rebound suppression which is absent when simulating virtual saccades (reproduced—as in the present study—by manipulating the retinal flow alone). "
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    • "Given the existence of a strong P1 response after fixation and that the modulation of its peak amplitude is given by the amplitude of the preceding saccade; our results suggest that for fERPs the P1 is generated by a perceptual component related to the processing of a stimulus at fixation, and by a saccade component or lambda potential generated by brain activity associated with eye movements (Thickbroom et al., 1991; Yagi, 1981). This is consistent with previous neurophysiological reports in humans and monkeys that show the existence of saccadic related responses locked to the onset of eye movements (Fourment et al., 1976; Rajkai et al., 2008; Skrandies and Laschke, 1997; but see also Ossandón et al., 2010, for an experiment in which clear visual components were absent when subjects performed saccades on a homogeneously gray screen). For comparison, we implemented a simple fixed-gaze paradigm using faces taken from the visual scenes. "
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