Lower layers in the motor cortex are more effective targets for penetrating microelectrodes in cortical prostheses

Abstract

Improving cortical prostheses requires the development of recording neural interfaces that are efficient in terms of providing maximal control information with minimal interface complexity. While the typical approaches have targeted neurons in the motor cortex with multiple penetrating shanks, an alternative approach is to determine an efficient distribution of electrode sites within the layers of the cortex with fewer penetrating shanks. The objective of this study was to compare unit activity in the upper and lower layers of the cortex with respect to movement and direction in order to inform the design of penetrating microelectrodes. Four rats were implanted bilaterally with multi-site single-shank silicon microelectrode arrays in the neck/shoulder region of the motor cortex. We simultaneously recorded unit activity across all layers of the motor cortex while the animal was engaged in a movement direction task. Localization of the electrode array within the different layers of the cortex was determined by histology. We denoted units from Layers 2 and 3 and units as upper layer units, and units from Layers 5 and 6 as lower layer units. Analysis of unit spiking activity demonstrated that both upper and lower layers enciode movement and direction information. Unit responses in either cortical layer of the cortex were not preferentially associated with contralateral or ipsilateral movement. Aggregate analysis (633 neurons) and best session analysis (75 neurons) indicated that units in the lower layers (Layers 5,6) are more likely to encode direction information when compared to units in the upper layers (Layers 2,3) (p<0.05). These results suggest that electrode sites clustered in the lower layers provide access to more salient control information for cortical neuroprostheses.

High gamma power in ECoG reflects cortical electrical stimulation effects on unit activity in layers V/VI

“…Upon completion of the experiment, electrolytic lesions were made followed by histological analysis to determine the electrode site locations within the different cortical layers (Yazdan-Shahmorad et al, 2011a,b, Parikh et al, 2009). In all cases, electrodes extracted from the brain were intact and were kept attached to the skull/headcap (Figure 2b).…”

“…100μm coronal slices were stained with a standard cresyl-violet (Nissl) staining method (Figure 2a). Exact stereotaxic positions of lesion marks and probe tracts were identified by co-registering histological images to the estimated probe locations from the images of the intact electrode arrays (Yazdan-Shahmorad et al, 2011a,b, Parikh et al, 2009). …”

Polarity of cortical electrical stimulation differentially affects neuronal activity of deep and superficial layers of rat motor cortex

“…On completion of the experiment, electrolytic lesions were made, followed by histologic analysis to determine the electrode site locations within the different cortical layers 22. In all cases, electrodes extracted from the brain were intact and were kept attached to the skull/headcap (Figure 2A and B).…”

The need for calcium imaging in nonhuman primates: New motor neuroscience and brain-machine interfaces

“…O-BMIs also provide a means to test how performance varies not only with how many, but also with which, neurons are recorded. While there have been prior electrode-based investigations of how movement-related information varies by cell type (Kaufman, Churchland, and Shenoy 2013) or cortical depth (Parikh, Marzullo, and Kipke 2009; Markowitz et al 2011), this approach is limited to either small ensembles of neurons recorded by movable electrodes, or larger but fixed ensembles from higher electrode-count arrays. We’ve recently reported a cortical viewing chamber with a 1 cm diameter usable area (Trautmann et al 2015).…”