Goldfish were taught to swim away from an area of their tank if a green light appeared, to avoid receiving an electric shock. The Spanish scientists damaged the medial pallia in the telencephalon in the brain of the fish. This caused them to forget to avoid the shock. The area of the brain damage is associated with emotional memory.
The effects observed in this experiment have also been observed in mammals. The researchers conclude that the fish and land vertebrates have inherited the same function from our ancestors who lived 400 million years ago.
"The hippocampus¹ and the amygdala² are involved in avoidance learning in mammals."
"The medial and lateral pallia of actinopterygian³ fish have been proposed as homologous to the mammalian pallial amygdala and hippocampus, respectively, on the basis of neuroanatomical findings."
"This work was aimed at studying the effects of ablation of the medial telencephalic pallia (MP) and lateral telencephalic pallia (LP) in goldfish on the retention of a conditioned avoidance response previously acquired in two experimental conditions."
GOLDFISH LEARN TO AVOID ELECTRIC SHOCK
"An experiment of two-way avoidance conditioning was performed using a previous design of a fish shuttle box."
"The presentation of shock (used as an aversive stimulus) was completely overlapped with a previous green light presentation (used as a discriminative stimulus) to minimize the interstimulus temporal factor. ... Thus, the temporal separation between cue onset and shock onset was 15 sec."
DAMAGING TELENCEPHALON REDUCES ABILITY TO AVOID SHOCKS
"An MP lesion affected the retention of the avoidance response."
TELENCEPHALON INVOLVES EMOTIONAL LEARNING
"These data support the presence of two different systems of memory in fish, based on discrete telencephalic areas: the MP, involved in an emotional memory system; and the LP, involved in a spatial, relational, or temporal memory system."
"Close similarity between the function of homologous telencephalic pallial areas suggests that the forebrain of vertebrates contains a common, conserved pattern of basic organization."
FISH AND MAMMALS SHARE A COMMON ANCESTOR FOR MEMORY
"Ray-finned fishes and land vertebrates share a common ancestor that lived some 400 million years ago."
TELENCEPHALON EQUIVALENT TO AMYGDALA AND HIPPOCAMPUS
"These differential effects were similar to those produced by amygdalar and hippocampal lesions in mammals. We conclude that these specialized systems of memory could have appeared early during phylogenesis and could have been conserved throughout vertebrate evolution."
¹ Actinopterygian - ray-finned fishes, constituting a class of the bony fishes.
² Amygdala - perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.
³ Hippocampus- an area of brain associated with memory: a curved ridge of tissue in each cerebral hemisphere of the brain, concerned with basic drives, emotions, and short-term memory and forming part of the limbic system.