A method for localizing microelectrode trajectories in the macaque brain using MRI

Abstract

Magnetic resonance imaging (MRI) is often used by electrophysiologists to target specific brain regions for placement of microelectrodes. However, the effectiveness of this technique has been limited by few methods to quantify in three dimensions the relative locations of brain structures, recording chambers and microelectrode trajectories. Here we present such a method. After surgical implantation, recording chambers are fitted with a plastic cylinder that is filled with a high-contrast agent to aid in the segmentation of the cylinder from brain matter in an MRI volume. The resulting images of the filled cylinder correspond to a virtual cylinder that is projected along its long axisparallel to the trajectories of microelectrodes advanced through the recording chamber -through the three-dimensional image of the brain. This technique, which does not require a stereotaxic coordinate system, can be used to quantify the coverage of an implanted recording chamber relative to anatomical landmarks at any depth or orientation. We have used this technique in conjunction with Caret (Van Essen et al., 2001) and AFNI (Cox, 1996) brain mapping software to successfully localize several regions of macaque cortex, including the middle temporal area, the lateral intraparietal area and the frontal eye field, and one subcortical structure, the locus coeruleus, for electrophysiological recordings.

Relationships between Pupil Diameter and Neuronal Activity in the Locus Coeruleus, Colliculi, and Cingulate Cortex

“…For CGp recordings, we targeted areas 31 and 23, in the posterior cingulate gyrus (~7–11 mm below cortical surface). Both brain regions were targeted using magnetic resonance imaging and custom software (Kalwani et al, 2009) as well as by listening for characteristic patterns of white and gray matter during recordings. Recordings were conducted using either single-contact glass-coated tungsten electrodes (Alpha-Omega) or multicontact linear electrode arrays (V-probe, Plexon).…”

“…(D, E) Schematic of a coronal section of the macaque brain showing structures typically encountered along our electrode tracts to ACC (D; adapted from (Paxinos et al, 2008), Plate 16, Interaural 33.60, bregma 11.70) or CGp (E; adapted from (Paxinos et al, 2008), Plate 89, Interaural 0.75, bregma -21.15). Lightly shaded yellow regions in (A) and (C) correspond to the three-dimensional projections of the recording cylinder (Kalwani et al, 2009). Arrows in (B), (D), and (E) show approximate electrode tracts.…”

Systematic mapping of the monkey inferior colliculus reveals enhanced low frequency sound representation

“…The visibility of morphological features of the IC on the scan and our ability to estimate the position of the cylinder and electrodes on the scan also influence the accuracy with which recording locations could be reconstructed. Reconstructing the borders of the IC via MRI scan using similar techniques has been estimated to be accurate to the nearest 1 mm (Kalwani et al 2009). …”

Recent refinements to cranial implants for rhesus macaques (Macaca mulatta)

“…Failure of the implant can lead to additional surgeries to repair or replace the implant, and even to euthanasia if the monkey can no longer participate in neurophysiological experiments. The spread of infection to the dura is also a serious concern because it can endanger the health of experimental animals, delay experiments, promote the formation of scar tissue and cause pain as the electrode penetrates the inflamed dura 6,12,19 . Other rare but possible complications that arise from the spread of a local infection include meningitis and brain abscesses 20 .…”