In an article, Thinking about Not-Thinking, the authors compare brain scans of Zen practitioners and people untrained in meditation. To explain their experiment, they first describe the nature of the meditation:
Zen meditation, in particular, is traditionally associated with a mental state of full awareness but reduced conceptual content, to be attained via a disciplined regulation of attention and bodily posture Buddhist meditative exercise has its roots in the metaphysical tenet of emptiness In cognitive terms, the attempt at mental regulation through meditation involves developing a progressive familiarity with the interplay of voluntary attention (often directed to the breath or posture) and the spontaneous conceptual processing that appears in its fractures, a process facilitated by the adoption of a stable seated posture and a quiet environment. It should also be noted that while (some) practices attempts to promote absorption and sensory withdrawal Zen meditation prescribes a vigilant attitude by a certain degree of active tension and by keeping the eyes open; mental withdrawal from the environment is considered as promoting a state of dreaminess and lack of clarity counterproductive to the meditative pursuit..
So we are looking at attempts to get rid of thoughts but remain in contact with the world and alert. This appears to be a special sort of consciousness that uses the default network. The default network is a group of brain regions that are active when the brain is not engaged in any mental or physical goal. It is the free wheeling activity of the idle brain. The network is often associated with daydreaming or free stream of consciousness. It appears that the Zen practitioners control the activity of this network so that the mind does not wander. Without goals, random thoughts or memories, there is not much left for the mind to do except just be alert. This is reported to result in a particular state:
According to this view, reality is originally devoid of ontological properties and it is only via an incessant and largely unconscious habit of emotional self-reference and categorization that a conceptual structure is created and ultimately reified; a process necessary for daily life, but that also tends to condition the individual into predefined patterns of thoughts, feelings, and behaviors. Meditation is believed to counteract this tendency in favor of a condition of equanimity where the provisional nature of ones own conceptual structure is realized, bringing about a greater freedom of thought and action as well as a decreased sense of self-attachment.
I envision this is a consciousness that is all warmed up and ready to go but is idling and just not engaged with normal life. It seems a somewhat different consciousness compared to the normal awake states (with varying levels of awareness) or dreams.