As discussed, the cerebellum cannot ‘feel’ itself, for the current threshold of detection is similar to the current threshold of behavioral (motor) elicitation (Doty 1969, 2007), and thus the cerebellum per se lacks the circuitry to exhibit consciousness [which is based on the activation of neurons that store declarative information, as reported by human subjects during electrical discharge of their temporal lobes, Penfield 1975]. Furthermore, the evocation of conscious impressions has never been reported for the cerebellum (Miterko et al. 2019; Ponce et al. 2022); moreover, the neurons in the cerebellum do not encode declarative routines, but instead convert declarative information (as housed in the neocortex) into executable motor code (Tehovnik et al. 2021).

In M1 of the macaque monkey, the current threshold for detection of electrical current is comparable to the current threshold for the induction of a motor response (Figure 20, Doty 1965, 1969)[1]. Based on the known anatomy of M1 this makes sense, since in the deepest layers of M1 many of the neurons form the pyramidal tract, which sends projections to the motor neurons in the brain stem and spinal cord and which, once activated, elicits muscle contractions (Sherrington 1906; Vanderwolf 2007). That consciousness is partitioned in the neocortex should not be of surprise, since the association areas of the neocortex are isolated synaptically from the motor system, by not sending direct projections into the pyramidal tract for immediate action; this is especially true of the temporal and orbital cortices whose neurons store object information related to vision, sound, taste, and smell (Brecht and Freiwald 2012; Bruce et al. 1981; Freiwald and Tsao 2010; Rolls 2004; Schwarzlose et al. 2005; Schwiedrzik, Freiwald et al. 2015).

Furthermore, areas of the neocortex that are involved in immediate action such as the frontal eye fields for the initiation of saccadic eye movements and area MT (the medial temporal cortex) for the initiation of visual pursuit are well-connected to the motor system (Figure 20). The frontal eye fields send direct projection to the saccade generator in the brain stem even bypassing the superior colliculus, and area MT (which also bypasses the superior colliculus) sends direct projections to the pons for immediate pursuit of visual targets (Schiller and Tehovnik 2015). This direct connectivity to the brain stem motor system suggests that these regions play a minimal role in conscious reflection, and a major role in the rapid execution of motor responses, much like M1 (Doty 1965, 1969)[2].

Also, neocortical areas that are more directly connected to the motor apparatus in the brain stem are more resistant to interference by an animal’s ongoing behavior (Tehovnik and Slocum 2004). Monkeys were required to actively fixate a visual target, such that breaking fixation would cause the loss of a juice reward, and electrical stimulation was delivered to the neocortex to see if the stimulation could dislodge the eyes from the fixation spot. It was found that when stimulation was delivered to the frontal eye fields, the threshold to break fixation was increased by three-times when compared to stimulation in the absence of active fixation. When the same experiment was done for the medial eye fields and area V1 it was found that the current threshold increased by 16-times and by over 40-times, respectively (Figure 20, Tehovnik et al. 2003a). Both the medial eye fields and area V1 are poorly connected to the saccade generator in the brain stem, as compared to the robust connectivity of the frontal eye fields[3]. And when such active fixation experiments are done in the superior colliculus, the current threshold increases by twice (Sparks and Mays 1983), and if the same experiment is done in the brain stem saccade generator there is no behavioral interference by the animal (Cohen and Komatsuzuki 1972), since in the case of the brain stem the output circuits are being activated directly. Likewise, stimulation of cerebellar circuits cannot be overridden by an animal (Noda and Fujikado 1987a; Noda et al. 1991). Thus, for a particular brain area, the less affected an area’s current threshold to an animal’s ongoing behavior, the less dedicated is the area to the conscious state of an animal. Indeed, when the motor neurons are activated, the conscious state of an animal can no longer intervene in the response.

Based on the idea that both M1 and the cerebellum are part of an unconscious network, it is noteworthy that damage to either M1 or the cerebellum disables a musician’s ability to play an instrument (Holms 1922; Nudo 2013; Watson 2006). But one of the differences between damage of M1 and the cerebellum is that M1 damage causes a specific body part to be affected according to the functional topography—i.e., whether the damage is to the face, the hand, or the leg representation—while damage of the cerebellar cortex needs to be diffuse to interfere maximally with the way movements are initiated from M1 (Nudo 2013; Thach et al. 1992). Based on this, it is presumed that M1 and the cerebellum are relatively independent of consciousness, unlike most regions of the neocortex (Doty 1969, 2007). It therefore follows that accomplished musicians deliver their talents using mainly unconscious networks: when an accomplished musician thinks about playing a violin, M1 is not active; whereas when the musician moves his fingers to play an instrument, M1 becomes active (as studied with fMRI, Watson 2006). Perhaps, the same is true of accomplished athletes and scientists. To date no one knows how Einstein came up with E = mc^2, and after dissecting his brain there was no progress on this front either (Kremer 2015).

Summary:

1. Unconscious networks in the neocortex send pyramidal fibres directly to the motor neurons of the brain stem and spinal cord.

2. M1 is the unconscious network for the skeletomotor system, and the frontal eye fields and the middle temporal cortex (area MT) are the unconscious networks for the oculomotor system.

3. The unconscious networks of the neocortex and those of the cerebellum mediate the execution of overlearned behaviors, such as an athlete running down a 100-meter track or an accomplished violinist playing his instrument or a scientist coming up with E = mc^2. But remember, to achieve this level of performance, many years of conscious effort (i.e., learning) precedes the final act of greatness.

Footnotes:

[1] When electrical stimulation is delivered to most areas of the neocortex currents can be detected perceptually, i.e., the currents are subthreshold to the evocation of a motor response (Bartlet and Doty 1980; Bartlett, Doty et al. 2005; Doty 1965, 1969, 2007; Doty et al. 1980; Koivuniemiand Otto2012; Murphey and Maunsell 2007, 2008; Rutledge and Doty 1962; Tehovnik and Slocum 2013). And in humans the effect of such currents can be described verbally (Penfield 1958, 1959, 1975; Penfield and Rasmussen 1952; Murphey et al. 2009).

[2] In the case of the cerebellum, much like area M1, it is intimately connected to the motor system as evidenced by having neurons that exhibit a rate code, and that routinely response to stimulation currents well under 10 μA, as studied in behaving primates (Tehovnik et al. 2021).

[3] Note that the excitability of the fibres mediating the saccadic eye movements elicited from the frontal eye field, medial eye fields, and area V1 are comparable (based on chronaxie measures), which indicates that any differences between these areas is due to the excitability of their down-stream synapses (Tehovnik and Sommer 1997; Tehovnik et al. 2003b).

Figure 20. The neocortex of the macaque monkey. Regions indicated include V1, MT (medial temporal cortex), M1, MEF (medial eye fields), FEF (frontal eye fields), and orbital and temporal cortices. Ocular functionality is indicated by ‘eye’, and skeleto-motor functionality is indicated by ‘face’, ‘hand’, and ‘leg’.