Synaptic Connections

“The Human Brain”, by myPerspectives, is an informative article that claims that the brain is a complex organ that is truly impressive. The brain is a key part of the central nervous system, that controls the entire body’s activities, to simple things such as breathing. These actions are fired through neurons, that quickly travel through the spinal cord. Surprisingly, the brain transmits these messages at an unimaginable rate, at 150 miles per hour, through 85 billion cells, called neurons. These neurons can form up to 10,000 synapses, or connections to each other. By itself, the brain can create billions of synapses, which change the structure of the brain every time new information is learned. However, there is still much that scientists

* Second, research has shown that damage to incoming sensory pathways or the destruction of brain tissue can lead to neural reorganization.

The concept of neuroplasticity has long been questioned. The term of “neuroplasticity” did not even come about until the mid-late 20th century. When the term “plastic” was used to describe the brain by a select few neuroscientists, they were laughed at and the term was never thought of as a description for the human brain. The human brain was seen as a closed circuit and one that once you had it, you definitely had it. Scientists thought the brain would not develop anymore past a certain point in your life. Norman Doidge brings the concept of neuroplasticity into reality in his book “The Brain that Changes Itself,” a book about the triumphs in the frontier of brain science.

Doctor Linqun Luo is a professor here at Stanford and currently teaches neurobiology and does research as the principal investigator in the Luo Lab as a member of the Howard Hughes Medical Institute. His primary research area is the human brain focusing on neural circuits and how they function, how precise are the connections, how they develop. To this end his lab is using fly and mouse models to study their various circuits, centering mainly on the olfactory, and exploring the early development of neural networks in mammals (Luo Lab Bio). In order to write this commentary on the topic “How do neurons connect with each other”, I have chosen two pieces to read. The first, from Science magazine, outlines the main issues, goals, and paths the world is taking to understand to understand neuroscience including the research being done to answer the question in his topic. The second paper, from Cell Press, is a much more technical paper which outlines one of the pathways Luo isolated in the olfactory cortex of mice and how their neurons may connect.

Anterograde Amnesia does not have a specific age of onset, but can occur when one experiences damage to the hippocampus through viral or bacterial infections, seizures, strokes, or restricted blood flow. In a study by Clark, Broadbent, Zola, and Squire (2002), rats who had part of their hippocampus area removed experienced anterograde amnesia as opposed to the control group who did not when they were placed in a food judgement task. In this task, rats were given different food each day, but there was one piece of food that remained constant. Here, the lesion rats did not gain a preference or liking towards a specific food. Meanwhile, the control group gained a preference

Some neuroscientists have made educated guesses as to the nature of this deletion, and there has been relative consensus that microglia, being part of the immune system, remove the synapses because they appear to be either unnecessary or damaged. This abnormal synaptic pruning could be a significant source of the symptoms of schizophrenia. If this mutation is genetic, then perhaps it could be corrected by sophisticated forms of genetic engineering. Loose associations have also been found between the genes that influence synaptic pruning and those that influence autism and Aspergers disorder. Pruning is also highly dependent on experience [4]. Neural plasticity reaches its peak during childhood and before synaptic pruning begins. Thus, if a child begins to learn a language or any other complex function before synaptic pruning, that function will be deemed important and the neural connections pertaining to it will be kept and strengthened. This gives new meaning to the saying “use it or lose it.” Experiences during and before synaptic pruning are perhaps some of the most important in development, because they directly affect brain function for the rest of the subject’s life. It is thought that connections deleted during pruning cannot be regained. "The fact that there are more connections [in a child's brain] allows things to be moved around," said physiologist Ian Campbell from the

Synaptic consolidation suggests that memory can exists in two ways, short term and long term. Short term memories must either transfer to long term memory or be lost (Bramham & Messaoudi, 2005). Synaptic consolidation occurs quickly, in the first few hours following the encoding of a new stimulus (Bramham & Messaoudi, 2005). Reverberating neural activity in closed circuits allows memories of new experiences to be stored in the short term

Elly Nedivi, an Associate Professor of Neurobiology at the Picower Institute for Learning and Memory, with the help of her colleagues, discovered that a certain type of brain cell can remodel lost connections, or neural pathways. Previously, researchers had found large-scale changes in dendrite-length, but more importantly, they found that this dendrite growth was limited to a specific type of cell: the interneuron. The cortical neurons they studied shoThe Adult Brain Neurons Can Remodel Connections

Millions of people on this Earth struggle daily with diseases that lie out of their control. Some with the involuntary and gradual amnesia of loved ones, others with memories that plague and haunt them on the loneliest of nights, and more. These issues are ironically forgotten those unaffected, and all stem from the same place- the brain’s memory engram cells. Engram cells are encoded neural tissue that provides a trace of memory and therefore is responsible for memory retrieval (1). Working in the lab with the implantation of memories and manipulating said engram cells of rodents can, over time, develop into altering human cells and activating memory retrieval to

Synaptic plasticity refers to a process through which the brain undergoes neural changes due to alterations in synaptic strength. Many studies have demonstrated that these synapses have the ability to strengthen or weaken on account of synaptic activity. In other words, an increase in synaptic activity will further strengthen that connection, making it more sensitive to a particular stimulus. Conversely, a decrease in synaptic activity will weaken the connection such that it loses its sensitivity to a given stimulus. The neuronal events that result in the strengthening or weakening of a synapse are explained through two mechanisms – Long-Term Potentiation (LTP) and Long-Term Depression (LTD). In fact, scientists believe that the coupling of these two mechanisms essentially contributes to memory and learning of an individual.

Learning is a very important aspect of humans and creatures alike. Not only is it essential to the survival and adaption into this world but it also defines who we are as individuals (Schiller et al, 2010; Tronson & Taylor, 2007). Memories from past experiences shape the people that we are today. A crucial element to learning is memory, without it we would not be able to retain information. The process of memory is very distinct and consists of several different stages: acquisition of memory, consolidation, retrieval and then either reconsolidation or extinction (Debiec & Ledoux, 2004; Diergaarde, Schoffelmeer & De Vries, 2008). As memory is such a critical aspect of learning, it is no wonder that its distinct process has become the topic of much research in the neurobiological universe (Hupbach et al, 2007; Nader & Hardt, 2009).

Doctors and scientists dispute the exact role of the hippocampus, but agree that it has an essential role in the formation of new memories about personally experienced events. Some researchers prefer to consider the hippocampus as part of a larger medial temporal lobe memory system responsible for declarative memory. When a long-term, declarative memory is made, certain neuronal connections in the temporal lobe are strengthened, and others are weakened. These changes are fairly permanent, however some may take weeks or months before they are complete

Global CaMKKβ-/- mice generated by Peters et al were found to have male specific impaired spatial memory formation secondary to reduced spatial-training induced CREB activation, as well as impaired long term memory for the social transmission of food preferences secondary to the lack of late long term potentiation at the hippocampal area CA1 synapses (Peters et al. 2003; Mizuno et al. 2007). No difference was found in other types of hippocampus dependent long term memory, including contextual fear memory and passive avoidance, compared to wild-type mice suggesting that the formation of these long term memory types do not require the activation of CREB by CaMKKβ.

The authors took extracellular electrophysiological recording to examine the functional change from hippocampus on parabionts. They found isochronic parabionts stayed at baseline level for long-term potentiation, but can be maintained at above baseline level in heterochronic parabionts. From these functional results, they concluded that young blood is capable to potentiate synaptic plasticity in aged mice.