The human thalamus acts as the gatekeeper for sensory information in your brain. When you sleep, you do not hear, taste, feel or see. Consistent stimulus: the alarm clock ringing, a telephone, someone shaking you, will wake you up. So how does the human brain prevent casual stimulus from keeping you awake all night?
Human Thalamus: Sleep's Gatekeeper
During the five stages of sleep, your external perceptions shut down allowing your mind to go into sleep mode. The human thalamus receives external sensory signals and then acts as a relay to the cerebral cortex. It is the job of the thalamus to shut down this gateway during sleep, preventing the stimuli from transmitting to the cortex and letting you get a good night's sleep.
The human thalamus consists of dual-lobed grey matter cells which are located at the top of the brainstem above the hypothalamus.
Study of the human thalamus is ongoing; currently neurologists recognize that among its primary functions are:
- Relay of sensory signals to the cerebral cortex
- Receptor of auditory, physical and visual signals
- Motor control
- Does not receive information from the olfactory senses
- Connects different areas of the brain to each other, allowing sensory input to evoke physical or emotional responses
- Works with the hypothalamus to regulate sleep and waking
Karen Ann Quinlan
In 1975, Karen Ann Quinlan (age 21) went to a bar with some friends. Due to severe menstrual cramps, she'd been taking Dragon, Valium, and aspirin all day. At the bar, she ordered a few rounds of gin and tonic. Later that night, she passed out and suffered a cardiac arrest. Although her heart was restarted, Karen lapsed into a persistent vegetative state. Her family won the right to remove her from life support, but Karen could breathe on her own and survived until perishing from sepsis in 1985. When her brain was later studied, neurologists found that her cerebral cortex was intact and not extensively damaged. This flew contrary to previous vegetative state cases. Instead, it was the human thalamus that showed the greatest amount of damage. It was completely disconnected from the cerebral cortex. The human thalamus is connected with consciousness as it provides the gatekeeper for all sensory input. Although Karen could sleep, wake and breathe on her own, she could not fix her attention, feel sensation or show any apparent conscious thought.
Damaged Human Thalamus
If the human thalamus is damaged physically or neurologically (stroke, accident, medications or genetics) it can lead to problems with sleeping, pain perception, memory issues, sensory impairment and more. Many sleep disorders are related to activity in the thalamic region. The type of problem is also directly related to where the damage is located within the thalamus.
Neurological research, sleep studies and more continue to deepen the understanding of the brain and how it functions. While the thalamus may be the gatekeeper to sleep, it provides many complex processes associated with sensory input and conscious reaction.