Recent advances in multi-electrode array technology have made it possible to monitor large neuronal ensembles at cellular resolution. In humans, however, current approaches either restrict recordings to only a few neurons per penetrating electrode or combine the signals of thousands of neurons in local field potential (LFP) recordings. Here, we describe a new probe variant and set of techniques which enable simultaneous recording from over 200 well-isolated cortical single units in human participants during intraoperative neurosurgical procedures using silicon Neuropixels probes. We characterized a diversity of extracellular waveforms with eight separable single unit classes, with differing firing rates, positions along the length of the linear electrode array, spatial spread of the waveform, and modulation by LFP events such as interictal discharges and burst suppression. While some additional challenges remain in creating a turn-key recording system, high-density silicon arrays provide a path for studying humanspecific cognitive processes and their dysfunction at unprecedented spatiotemporal resolution.Major technological advances in the past decade have led to a revolution in the neurosciences.Many research programs now routinely rely on the analysis of single-neuron action potentials from hundreds and even thousands of neurons, which provide a rich understanding of the coordinated activity of large neuronal ensembles that underlie sensory, motor, and cognitive operations [1][2][3][4] . While these developments have been most pronounced in animal models, there have been parallel, albeit slower, advances in the ability to record from single neurons in humans. Single-unit recordings in humans have been performed since the mid-1950s 5-8 , and were foundational in understanding the role of neural circuits in neurologic disease. For example, such techniques helped to establish an understanding of the relationship between .

Summary Many evolutionary years separate humans and macaques, and whereas the amygdala and cingulate-cortex evolved to enable emotion and cognition in both, an evident functional gap exists. Although it was traditionally attributed to differential neuroanatomy, functional differences might also arise from coding mechanisms. Here, we find that human neurons better utilize information capacity (efficient coding) than macaque neurons, in both regions; and that cingulate neurons are more efficient than amygdala neurons, in both species. In contrast, we find more overlap in the neural vocabulary and more synchronized activity (robustness coding) in monkeys in both regions, and in the amygdala of both species. Our findings demonstrate a tradeoff between robustness and efficiency across species and regions. We suggest that this tradeoff can contribute to differential cognitive functions between species, and underlie the complementary roles of the amygdala and the cingulate-cortex. In turn, it can contribute to fragility underlying human psychopathologies.

Recent advances in multi-electrode array technology have made it possible to monitor large neuronal ensembles at high resolution. In humans, however, current approaches either restrict recordings to only a few neurons per penetrating electrode or combine the signals of thousands of neurons in local field potential (LFP) recordings. Here, we describe a set of techniques which enable simultaneous recording from over 200 well-isolated cortical single units in human participants during intraoperative neurosurgical procedures using Neuropixels silicon probes. We characterized a diversity of extracellular waveforms with eight separable single unit classes, with differing firing rates, positions along the length of the linear electrode array, spatial spread of the waveform, and modulation by LFP events such as inter-ictal discharges and burst suppression. While some additional challenges remain in creating a turn-key system capable of recording, Neuropixels technology could pave the way to studying human-specific cognitive processes and their dysfunction at unprecedented spatiotemporal resolution.