What is a Neurotransmitter?

Neurons are nerve cells that are located in the human nervous system. Neurotransmitters are involved in the process of neurotransmission, which refers to the process when the action potential triggers the presynaptic neuron to release neurotransmitters, which are then released into the synapse and then taken up by the receptors on the postsynaptic neuron. Neurotransmitters are brain chemicals that act as “messengers” transmitting information from one neuron to another and are released in the synapse – the gap between neurons – helping facilitate communication between neurons. Studying neurotransmitters is significant as understanding their roles and interactions contributes to investigating neural communication networks that enable cognition, emotion, and behavior in everyday life. Neurotransmitters are classified into two types – inhibitory neurotransmitters, which decrease the likelihood of a neuron firing by hyperpolarizing the neuron, and excitatory neurotransmitters, which increase and “excite” the likelihood of a neuron firing by depolarizing. Acetylcholine is a type of excitatory neurotransmitter that may play an important role in memory, learning, attention, arousal, and involuntary muscle movement, exciting certain neurons. Acetylcholine is specifically associated with muscular control and spatial memory and is found in the brain, spinal cord, and the peripheral nervous system. Acetylcholine is an agonist – any chemical that binds to a specific receptor and activates it – for ACh receptor sites, like all other neurotransmitters are endogenous agonists for receptor sites as part of our nervous system. The antagonist – a chemical (usually a drug) that blocks the receptor site and does not allow the effect of a neurotransmitter – of the Ach receptor site is scopolamine. This response will discuss the neurotransmitter acetylcholine and its effect on behaviors with regard to Antonova (2011).

Antonova (2011) aimed to investigate if scopolamine affected hippocampal activity in the creation of spatial memory. Participants were a sample of 20 healthy male adults with a mean age of 28. They were randomly allocated into two conditions: the scopolamine group, in which participants were injected with scopolamine 70 to 90 minutes before starting the task, and the placebo group, where they were injected with placebo 70 to 90 minutes prior to the beginning. The men were put into an fMRI where they were scanned while playing the “Arena task”, a complex virtual reality game in which the researchers observed how well the participants could create spatial memories. The goal of the game was to navigate around an arena to reach a pole; after they learned where the pole was located, the screen would go blank for 30 seconds. During this time, they were told to actively rehearse how to get to the pole in the arena, and when the arena reappeared, the participant was now at a new starting point in the arena. When the arena reappeared, the participant was now at a new starting point in the arena and they had to use their spatial memory to determine how to get to the location of the pole. Most importantly, they were first trained to ensure that they were comfortable with the use of the joystick & that they understood the rules of the game; after they were trained, they took part in the experiment. Participants’ brain activity was measured using an fMRI for 6 trials. 3 to 4 weeks later, participants redid the test while receiving the opposite treatment to the original study, indicating a repeated measures design. Consequently, when participants were injected with scopolamine, they demonstrated a significant reduction in the activation of the hippocampus compared to when they received a placebo.

The results suggest that acetylcholine could play a key role in the encoding of spatial memories in humans; although the scopolamine group had a higher rate of error, it was not significantly different between the two groups. Instead, the hippocampus activity was significantly distinct between them, which implies that scopolamine blocked the ‘scopolamine’ participants’ receptor sites of acetylcholine, which is associated with spatial memory, decreasing the hippocampus activity.