Methods for Voltage-Sensitive Dye Imaging of Rat Cortical Activity With High Signal-to-Noise Ratio

Abstract

We describe methods to achieve high sensitivity in voltage-sensitive dye (VSD) imaging from rat barrel and visual cortices in vivo with the use of a blue dye RH1691 and a high dynamic range imaging device (photodiode array). With an improved staining protocol and an off-line procedure to remove pulsation artifact, the sensitivity of VSD recording is comparable with that of local field potential recording from the same location. With this sensitivity, one can record from approximately 500 individual detectors, each covering an area of cortical tissue 160 microm in diameter (total imaging field approximately 4 mm in diameter) and a temporal resolution of 1,600 frames/s, without multiple-trial averaging. We can record 80-100 trials of intermittent 10-s trials from each imaging field before the VSD signal reduces to one half of its initial amplitude because of bleaching and wash-out. Taken together, the methods described in this report provide a useful tool for visualizing evoked and spontaneous waves from rodent cortex.

Voltage-sensitive dye imaging reveals shifting spatiotemporal spread of whisker-induced activity in rat barrel cortex

“…The spatial profile of the VSD images showed initial focal activity roughly the diameter of a barrel column (ϳ400 m) followed by a rapid horizontal spread preferentially within a whisker row and then to surrounding cortex, in agreement with previous studies (Kleinfeld and Delaney 1996;Petersen and Sakmann 2001). Similarly, in previous studies using electrophysiology and VSD imaging of barrel cortex, it was shown that responses start in layer 4 of barrels, progress vertically directly above the barrel into layer 2/3, and then spread horizontally in layer 2/3 in a "pagoda like" manner (Kleinfeld and Delaney 1996;Lippert et al 2007;Petersen and Sakmann 2001;Tanifuji et al 1994).…”

“…VSD imaging measures changes in membrane potential over large populations of neurons primarily in layer 2/3 of cortex (Civillico and Contreras 2006;Ferezou et al 2006;Jin et al 2002;Kleinfeld and Delaney 1996;Lippert et al 2007) and is thus useful for revealing the time and spread of barrel responses as well as more distant subthreshold modulatory response. Civillico and Contreras (2006) used this method to study barrel fields in mice and found, surprisingly, only suppressive effects in multiwhisker responses.…”

Optical imaging of plastic changes induced by fear conditioning in the auditory cortex

“…It has been reported that optical imaging may record neuronal responses mainly from layers II and III in the cerebral cortex (Horikawa et al 1996;Lippert et al 2006), implying that synaptic plasticity may have been induced in these layers of the auditory cortex in the present study. These results correspond to reports that layers II and III of the barrel cortex play an important role in cortical plastic changes (Huang et al 1998) and that LTP can be induced in the horizontal connections in layers II and III of the motor cortex (Hess et al 1996).…”

Cortico-cortical Communication Dynamics

“…Traditionally, this is called "spontaneous ongoing activity", as the sources of this activity are not known. This intrinsic activity is also communicated between cortical areas (Arieli et al, 1995;Lippert et al, 2007;Xu et al, 2007).…”

“…In principle, this may be possible in studies of anesthetized brains, where it is sometimes possible to capture the population of neurons bifurcating into an up-state (Figure 1). Then one can follow how the up-state spreads to populations of neurons in adjacent areas (Lilly, 1954;Lippert et al, 2007;Xu et al, 2007;Huang et al, 2010;Gao et al, 2012;Zheng and Yao, 2012). In contrast to sensory evoked activity, the spontaneous up-states may spread from different origins in the cortex.…”