Insights into cortical mechanisms of behavior from microstimulation experiments

Abstract

Even the simplest behaviors depend on a large number of neurons that are distributed across many brain regions. Because electrical microstimulation can change the activity of localized subsets of neurons, it has provided valuable evidence that specific neurons contribute to particular behaviors. Here we review what has been learned about cortical function from behavioral studies using microstimulation in animals and humans. Experiments that examine how microstimulation affects the perception of stimuli have shown that the effects of microstimulation are usually highly specific and can be related to the stimuli preferred by neurons at the stimulated site. Experiments that ask subjects to detect cortical microstimulation in the absence of other stimuli have provided further insights. Although subjects typically can detect microstimulation of primary sensory or motor cortex, they are generally unable to detect stimulation of most of cortex without extensive practice. With practice, however, stimulation of any part of cortex can become detected. These training effects suggest that some patterns of cortical activity cannot be readily accessed to guide behavior, but that the adult brain retains enough plasticity to learn to process novel patterns of neuronal activity arising anywhere in cortex.

Cortical neural populations can guide behavior by integrating inputs linearly, independent of synchrony

“…S2), as would be expected if the animals were directly detecting changes in neuronal activity and not the laser light. Shorter reaction times to cortical stimulation [∼150 ms minimum compared with ∼210 ms minimum in a visual task (23)] are further evidence that animals detect direct neuronal activation, as has been shown previously in a range of species and brain areas (24)(25)(26)(27)(28).…”

“…Electrical stimulation studies cannot examine network linearity, because pulsed current has a stronger effect than sustained current (48) and because there is a complex relationship between stimulation current and evoked spike count. However, the stimulation currents used likely evoked stronger activity than our near-threshold stimulation (27,49). In fact, frequency discrimination of both sensory and direct electrical stimuli is best with intensities well above the detection threshold (50).…”

Monopolar high-frequency language mapping: can it help in the surgical management of gliomas? A comparative clinical study

“…In fact, a more detailed neurophysiological understanding of the stimulation effects on the axons of different neurons is still lacking, and thus a different type of analysis is required to better elucidate this relationship. 21 A blinded comparison between the 2 stimulation modalities should be performed to address this issue in a more robust way. However, such a study is unlikely to be easily realized with appropriate statistical power for the following reasons.…”

Optical imaging of cortical networks via intracortical microstimulation

“…Studies that use electrical stimulation to evoke complex motor movements use less, with typical values being 300 Hz, 500 ms, and amplitudes ranging from 10 to 300 A depending on cortical area (Bruce et al 1985;Graziano et al 2002;Thier and Andersen 1998). Finally, awake behaving studies have found current detection thresholds to be around 10 A, or less with training, when intracortical microstimulation is applied to sensory cortices (Medina et al 2012;Murphey and Maunsell 2007;Ni and Maunsell 2010;O'Doherty et al 2009;Salzman et al 1990; for reviews, see Clark et al 2011;Histed et al 2013). For the parameters tested, cortical activation was dependent on both the current amplitude of a single pulse and the number of pulses.…”